move to src directory

27 files changed, 12764 insertions, 0 deletions

diff --git a/src/jinja2/__init__.py b/src/jinja2/__init__.py
new file mode 100644
index 0000000..9c46e49
--- /dev/null
+++ b/src/jinja2/__init__.py
@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2
+    ~~~~~~
+
+    Jinja is a template engine written in pure Python.  It provides a
+    Django inspired non-XML syntax but supports inline expressions and
+    an optional sandboxed environment.
+
+    Nutshell
+    --------
+
+    Here a small example of a Jinja template::
+
+        {% extends 'base.html' %}
+        {% block title %}Memberlist{% endblock %}
+        {% block content %}
+          <ul>
+          {% for user in users %}
+            <li><a href="{{ user.url }}">{{ user.username }}</a></li>
+          {% endfor %}
+          </ul>
+        {% endblock %}
+
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+__docformat__ = 'restructuredtext en'
+__version__ = "2.11.0.dev0"
+
+# high level interface
+from jinja2.environment import Environment, Template
+
+# loaders
+from jinja2.loaders import BaseLoader, FileSystemLoader, PackageLoader, \
+     DictLoader, FunctionLoader, PrefixLoader, ChoiceLoader, \
+     ModuleLoader
+
+# bytecode caches
+from jinja2.bccache import BytecodeCache, FileSystemBytecodeCache, \
+     MemcachedBytecodeCache
+
+# undefined types
+from jinja2.runtime import Undefined, ChainableUndefined, DebugUndefined, \
+     StrictUndefined, make_logging_undefined
+
+# exceptions
+from jinja2.exceptions import TemplateError, UndefinedError, \
+     TemplateNotFound, TemplatesNotFound, TemplateSyntaxError, \
+     TemplateAssertionError, TemplateRuntimeError
+
+# decorators and public utilities
+from jinja2.filters import environmentfilter, contextfilter, \
+     evalcontextfilter
+from jinja2.utils import Markup, escape, clear_caches, \
+     environmentfunction, evalcontextfunction, contextfunction, \
+     is_undefined, select_autoescape
+
+__all__ = [
+    'Environment', 'Template', 'BaseLoader', 'FileSystemLoader',
+    'PackageLoader', 'DictLoader', 'FunctionLoader', 'PrefixLoader',
+    'ChoiceLoader', 'BytecodeCache', 'FileSystemBytecodeCache',
+    'MemcachedBytecodeCache', 'Undefined', 'DebugUndefined',
+    'StrictUndefined', 'TemplateError', 'UndefinedError', 'TemplateNotFound',
+    'TemplatesNotFound', 'TemplateSyntaxError', 'TemplateAssertionError',
+    'TemplateRuntimeError',
+    'ModuleLoader', 'environmentfilter', 'contextfilter', 'Markup', 'escape',
+    'environmentfunction', 'contextfunction', 'clear_caches', 'is_undefined',
+    'evalcontextfilter', 'evalcontextfunction', 'make_logging_undefined',
+    'select_autoescape',
+]
diff --git a/src/jinja2/_compat.py b/src/jinja2/_compat.py
new file mode 100644
index 0000000..814d224
--- /dev/null
+++ b/src/jinja2/_compat.py
@@ -0,0 +1,124 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2._compat
+    ~~~~~~~~~~~~~~
+
+    Some py2/py3 compatibility support based on a stripped down
+    version of six so we don't have to depend on a specific version
+    of it.
+
+    :copyright: Copyright 2013 by the Jinja team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+import sys
+
+PY2 = sys.version_info[0] == 2
+PYPY = hasattr(sys, 'pypy_translation_info')
+_identity = lambda x: x
+
+
+if not PY2:
+    unichr = chr
+    range_type = range
+    text_type = str
+    string_types = (str,)
+    integer_types = (int,)
+
+    iterkeys = lambda d: iter(d.keys())
+    itervalues = lambda d: iter(d.values())
+    iteritems = lambda d: iter(d.items())
+
+    import pickle
+    from io import BytesIO, StringIO
+    NativeStringIO = StringIO
+
+    def reraise(tp, value, tb=None):
+        if value.__traceback__ is not tb:
+            raise value.with_traceback(tb)
+        raise value
+
+    ifilter = filter
+    imap = map
+    izip = zip
+    intern = sys.intern
+
+    implements_iterator = _identity
+    implements_to_string = _identity
+    encode_filename = _identity
+
+else:
+    unichr = unichr
+    text_type = unicode
+    range_type = xrange
+    string_types = (str, unicode)
+    integer_types = (int, long)
+
+    iterkeys = lambda d: d.iterkeys()
+    itervalues = lambda d: d.itervalues()
+    iteritems = lambda d: d.iteritems()
+
+    import cPickle as pickle
+    from cStringIO import StringIO as BytesIO, StringIO
+    NativeStringIO = BytesIO
+
+    exec('def reraise(tp, value, tb=None):\n raise tp, value, tb')
+
+    from itertools import imap, izip, ifilter
+    intern = intern
+
+    def implements_iterator(cls):
+        cls.next = cls.__next__
+        del cls.__next__
+        return cls
+
+    def implements_to_string(cls):
+        cls.__unicode__ = cls.__str__
+        cls.__str__ = lambda x: x.__unicode__().encode('utf-8')
+        return cls
+
+    def encode_filename(filename):
+        if isinstance(filename, unicode):
+            return filename.encode('utf-8')
+        return filename
+
+
+def with_metaclass(meta, *bases):
+    """Create a base class with a metaclass."""
+    # This requires a bit of explanation: the basic idea is to make a
+    # dummy metaclass for one level of class instantiation that replaces
+    # itself with the actual metaclass.
+    class metaclass(type):
+        def __new__(cls, name, this_bases, d):
+            return meta(name, bases, d)
+    return type.__new__(metaclass, 'temporary_class', (), {})
+
+
+try:
+    from urllib.parse import quote_from_bytes as url_quote
+except ImportError:
+    from urllib import quote as url_quote
+
+
+try:
+    from collections import abc
+except ImportError:
+    import collections as abc
+
+
+try:
+    from os import fspath
+except ImportError:
+    try:
+        from pathlib import PurePath
+    except ImportError:
+        PurePath = None
+
+    def fspath(path):
+        if hasattr(path, "__fspath__"):
+            return path.__fspath__()
+
+        # Python 3.5 doesn't have __fspath__ yet, use str.
+        if PurePath is not None and isinstance(path, PurePath):
+            return str(path)
+
+        return path
diff --git a/src/jinja2/_identifier.py b/src/jinja2/_identifier.py
new file mode 100644
index 0000000..2eac35d
--- /dev/null
+++ b/src/jinja2/_identifier.py
@@ -0,0 +1,2 @@
+# generated by scripts/generate_identifier_pattern.py
+pattern = '·̀-ͯ·҃-֑҇-ׇֽֿׁׂׅׄؐ-ًؚ-ٰٟۖ-ۜ۟-۪ۤۧۨ-ܑۭܰ-݊ަ-ް߫-߳ࠖ-࠙ࠛ-ࠣࠥ-ࠧࠩ-࡙࠭-࡛ࣔ-ࣣ࣡-ःऺ-़ा-ॏ॑-ॗॢॣঁ-ঃ়া-ৄেৈো-্ৗৢৣਁ-ਃ਼ਾ-ੂੇੈੋ-੍ੑੰੱੵઁ-ઃ઼ા-ૅે-ૉો-્ૢૣଁ-ଃ଼ା-ୄେୈୋ-୍ୖୗୢୣஂா-ூெ-ைொ-்ௗఀ-ఃా-ౄె-ైొ-్ౕౖౢౣಁ-ಃ಼ಾ-ೄೆ-ೈೊ-್ೕೖೢೣഁ-ഃാ-ൄെ-ൈൊ-്ൗൢൣංඃ්ා-ුූෘ-ෟෲෳัิ-ฺ็-๎ັິ-ູົຼ່-ໍ༹༘༙༵༷༾༿ཱ-྄྆྇ྍ-ྗྙ-ྼ࿆ါ-ှၖ-ၙၞ-ၠၢ-ၤၧ-ၭၱ-ၴႂ-ႍႏႚ-ႝ፝-፟ᜒ-᜔ᜲ-᜴ᝒᝓᝲᝳ឴-៓៝᠋-᠍ᢅᢆᢩᤠ-ᤫᤰ-᤻ᨗ-ᨛᩕ-ᩞ᩠-᩿᩼᪰-᪽ᬀ-ᬄ᬴-᭄᭫-᭳ᮀ-ᮂᮡ-ᮭ᯦-᯳ᰤ-᰷᳐-᳔᳒-᳨᳭ᳲ-᳴᳸᳹᷀-᷵᷻-᷿‿⁀⁔⃐-⃥⃜⃡-⃰℘℮⳯-⵿⳱ⷠ-〪ⷿ-゙゚〯꙯ꙴ-꙽ꚞꚟ꛰꛱ꠂ꠆ꠋꠣ-ꠧꢀꢁꢴ-ꣅ꣠-꣱ꤦ-꤭ꥇ-꥓ꦀ-ꦃ꦳-꧀ꧥꨩ-ꨶꩃꩌꩍꩻ-ꩽꪰꪲ-ꪴꪷꪸꪾ꪿꫁ꫫ-ꫯꫵ꫶ꯣ-ꯪ꯬꯭ﬞ︀-️︠-︯︳︴﹍-﹏＿𐇽𐋠𐍶-𐍺𐨁-𐨃𐨅𐨆𐨌-𐨏𐨸-𐨿𐨺𐫦𐫥𑀀-𑀂𑀸-𑁆𑁿-𑂂𑂰-𑂺𑄀-𑄂𑄧-𑅳𑄴𑆀-𑆂𑆳-𑇊𑇀-𑇌𑈬-𑈷𑈾𑋟-𑋪𑌀-𑌃𑌼𑌾-𑍄𑍇𑍈𑍋-𑍍𑍗𑍢𑍣𑍦-𑍬𑍰-𑍴𑐵-𑑆𑒰-𑓃𑖯-𑖵𑖸-𑗀𑗜𑗝𑘰-𑙀𑚫-𑚷𑜝-𑜫𑰯-𑰶𑰸-𑰿𑲒-𑲧𑲩-𑲶𖫰-𖫴𖬰-𖬶𖽑-𖽾𖾏-𖾒𛲝𛲞𝅥-𝅩𝅭-𝅲𝅻-𝆂𝆅-𝆋𝆪-𝆭𝉂-𝉄𝨀-𝨶𝨻-𝩬𝩵𝪄𝪛-𝪟𝪡-𝪯𞀀-𞀆𞀈-𞀘𞀛-𞀡𞀣𞀤𞀦-𞣐𞀪-𞣖𞥄-𞥊󠄀-󠇯'
diff --git a/src/jinja2/asyncfilters.py b/src/jinja2/asyncfilters.py
new file mode 100644
index 0000000..cf051dd
--- /dev/null
+++ b/src/jinja2/asyncfilters.py
@@ -0,0 +1,146 @@
+from functools import wraps
+
+from jinja2.asyncsupport import auto_aiter, auto_await
+from jinja2 import filters
+
+
+async def auto_to_seq(value):
+    seq = []
+    if hasattr(value, '__aiter__'):
+        async for item in value:
+            seq.append(item)
+    else:
+        for item in value:
+            seq.append(item)
+    return seq
+
+
+async def async_select_or_reject(args, kwargs, modfunc, lookup_attr):
+    seq, func = filters.prepare_select_or_reject(
+        args, kwargs, modfunc, lookup_attr)
+    if seq:
+        async for item in auto_aiter(seq):
+            if func(item):
+                yield item
+
+
+def dualfilter(normal_filter, async_filter):
+    wrap_evalctx = False
+    if getattr(normal_filter, 'environmentfilter', False):
+        is_async = lambda args: args[0].is_async
+        wrap_evalctx = False
+    else:
+        if not getattr(normal_filter, 'evalcontextfilter', False) and \
+           not getattr(normal_filter, 'contextfilter', False):
+            wrap_evalctx = True
+        is_async = lambda args: args[0].environment.is_async
+
+    @wraps(normal_filter)
+    def wrapper(*args, **kwargs):
+        b = is_async(args)
+        if wrap_evalctx:
+            args = args[1:]
+        if b:
+            return async_filter(*args, **kwargs)
+        return normal_filter(*args, **kwargs)
+
+    if wrap_evalctx:
+        wrapper.evalcontextfilter = True
+
+    wrapper.asyncfiltervariant = True
+
+    return wrapper
+
+
+def asyncfiltervariant(original):
+    def decorator(f):
+        return dualfilter(original, f)
+    return decorator
+
+
+@asyncfiltervariant(filters.do_first)
+async def do_first(environment, seq):
+    try:
+        return await auto_aiter(seq).__anext__()
+    except StopAsyncIteration:
+        return environment.undefined('No first item, sequence was empty.')
+
+
+@asyncfiltervariant(filters.do_groupby)
+async def do_groupby(environment, value, attribute):
+    expr = filters.make_attrgetter(environment, attribute)
+    return [filters._GroupTuple(key, await auto_to_seq(values))
+            for key, values in filters.groupby(sorted(
+                await auto_to_seq(value), key=expr), expr)]
+
+
+@asyncfiltervariant(filters.do_join)
+async def do_join(eval_ctx, value, d=u'', attribute=None):
+    return filters.do_join(eval_ctx, await auto_to_seq(value), d, attribute)
+
+
+@asyncfiltervariant(filters.do_list)
+async def do_list(value):
+    return await auto_to_seq(value)
+
+
+@asyncfiltervariant(filters.do_reject)
+async def do_reject(*args, **kwargs):
+    return async_select_or_reject(args, kwargs, lambda x: not x, False)
+
+
+@asyncfiltervariant(filters.do_rejectattr)
+async def do_rejectattr(*args, **kwargs):
+    return async_select_or_reject(args, kwargs, lambda x: not x, True)
+
+
+@asyncfiltervariant(filters.do_select)
+async def do_select(*args, **kwargs):
+    return async_select_or_reject(args, kwargs, lambda x: x, False)
+
+
+@asyncfiltervariant(filters.do_selectattr)
+async def do_selectattr(*args, **kwargs):
+    return async_select_or_reject(args, kwargs, lambda x: x, True)
+
+
+@asyncfiltervariant(filters.do_map)
+async def do_map(*args, **kwargs):
+    seq, func = filters.prepare_map(args, kwargs)
+    if seq:
+        async for item in auto_aiter(seq):
+            yield await auto_await(func(item))
+
+
+@asyncfiltervariant(filters.do_sum)
+async def do_sum(environment, iterable, attribute=None, start=0):
+    rv = start
+    if attribute is not None:
+        func = filters.make_attrgetter(environment, attribute)
+    else:
+        func = lambda x: x
+    async for item in auto_aiter(iterable):
+        rv += func(item)
+    return rv
+
+
+@asyncfiltervariant(filters.do_slice)
+async def do_slice(value, slices, fill_with=None):
+    return filters.do_slice(await auto_to_seq(value), slices, fill_with)
+
+
+ASYNC_FILTERS = {
+    'first':        do_first,
+    'groupby':      do_groupby,
+    'join':         do_join,
+    'list':         do_list,
+    # we intentionally do not support do_last because that would be
+    # ridiculous
+    'reject':       do_reject,
+    'rejectattr':   do_rejectattr,
+    'map':          do_map,
+    'select':       do_select,
+    'selectattr':   do_selectattr,
+    'sum':          do_sum,
+    'slice':        do_slice,
+}
diff --git a/src/jinja2/asyncsupport.py b/src/jinja2/asyncsupport.py
new file mode 100644
index 0000000..d225962
--- /dev/null
+++ b/src/jinja2/asyncsupport.py
@@ -0,0 +1,264 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.asyncsupport
+    ~~~~~~~~~~~~~~~~~~~
+
+    Has all the code for async support which is implemented as a patch
+    for supported Python versions.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import asyncio
+import inspect
+from functools import update_wrapper
+
+from jinja2.environment import TemplateModule
+from jinja2.runtime import LoopContext
+from jinja2.utils import concat
+from jinja2.utils import internalcode
+from jinja2.utils import Markup
+from jinja2.utils import missing
+
+
+async def concat_async(async_gen):
+    rv = []
+    async def collect():
+        async for event in async_gen:
+            rv.append(event)
+    await collect()
+    return concat(rv)
+
+
+async def generate_async(self, *args, **kwargs):
+    vars = dict(*args, **kwargs)
+    try:
+        async for event in self.root_render_func(self.new_context(vars)):
+            yield event
+    except Exception:
+        yield self.environment.handle_exception()
+
+
+def wrap_generate_func(original_generate):
+    def _convert_generator(self, loop, args, kwargs):
+        async_gen = self.generate_async(*args, **kwargs)
+        try:
+            while 1:
+                yield loop.run_until_complete(async_gen.__anext__())
+        except StopAsyncIteration:
+            pass
+    def generate(self, *args, **kwargs):
+        if not self.environment.is_async:
+            return original_generate(self, *args, **kwargs)
+        return _convert_generator(self, asyncio.get_event_loop(), args, kwargs)
+    return update_wrapper(generate, original_generate)
+
+
+async def render_async(self, *args, **kwargs):
+    if not self.environment.is_async:
+        raise RuntimeError('The environment was not created with async mode '
+                           'enabled.')
+
+    vars = dict(*args, **kwargs)
+    ctx = self.new_context(vars)
+
+    try:
+        return await concat_async(self.root_render_func(ctx))
+    except Exception:
+        return self.environment.handle_exception()
+
+
+def wrap_render_func(original_render):
+    def render(self, *args, **kwargs):
+        if not self.environment.is_async:
+            return original_render(self, *args, **kwargs)
+        loop = asyncio.get_event_loop()
+        return loop.run_until_complete(self.render_async(*args, **kwargs))
+    return update_wrapper(render, original_render)
+
+
+def wrap_block_reference_call(original_call):
+    @internalcode
+    async def async_call(self):
+        rv = await concat_async(self._stack[self._depth](self._context))
+        if self._context.eval_ctx.autoescape:
+            rv = Markup(rv)
+        return rv
+
+    @internalcode
+    def __call__(self):
+        if not self._context.environment.is_async:
+            return original_call(self)
+        return async_call(self)
+
+    return update_wrapper(__call__, original_call)
+
+
+def wrap_macro_invoke(original_invoke):
+    @internalcode
+    async def async_invoke(self, arguments, autoescape):
+        rv = await self._func(*arguments)
+        if autoescape:
+            rv = Markup(rv)
+        return rv
+
+    @internalcode
+    def _invoke(self, arguments, autoescape):
+        if not self._environment.is_async:
+            return original_invoke(self, arguments, autoescape)
+        return async_invoke(self, arguments, autoescape)
+    return update_wrapper(_invoke, original_invoke)
+
+
+@internalcode
+async def get_default_module_async(self):
+    if self._module is not None:
+        return self._module
+    self._module = rv = await self.make_module_async()
+    return rv
+
+
+def wrap_default_module(original_default_module):
+    @internalcode
+    def _get_default_module(self):
+        if self.environment.is_async:
+            raise RuntimeError('Template module attribute is unavailable '
+                               'in async mode')
+        return original_default_module(self)
+    return _get_default_module
+
+
+async def make_module_async(self, vars=None, shared=False, locals=None):
+    context = self.new_context(vars, shared, locals)
+    body_stream = []
+    async for item in self.root_render_func(context):
+        body_stream.append(item)
+    return TemplateModule(self, context, body_stream)
+
+
+def patch_template():
+    from jinja2 import Template
+    Template.generate = wrap_generate_func(Template.generate)
+    Template.generate_async = update_wrapper(
+        generate_async, Template.generate_async)
+    Template.render_async = update_wrapper(
+        render_async, Template.render_async)
+    Template.render = wrap_render_func(Template.render)
+    Template._get_default_module = wrap_default_module(
+        Template._get_default_module)
+    Template._get_default_module_async = get_default_module_async
+    Template.make_module_async = update_wrapper(
+        make_module_async, Template.make_module_async)
+
+
+def patch_runtime():
+    from jinja2.runtime import BlockReference, Macro
+    BlockReference.__call__ = wrap_block_reference_call(
+        BlockReference.__call__)
+    Macro._invoke = wrap_macro_invoke(Macro._invoke)
+
+
+def patch_filters():
+    from jinja2.filters import FILTERS
+    from jinja2.asyncfilters import ASYNC_FILTERS
+    FILTERS.update(ASYNC_FILTERS)
+
+
+def patch_all():
+    patch_template()
+    patch_runtime()
+    patch_filters()
+
+
+async def auto_await(value):
+    if inspect.isawaitable(value):
+        return await value
+    return value
+
+
+async def auto_aiter(iterable):
+    if hasattr(iterable, '__aiter__'):
+        async for item in iterable:
+            yield item
+        return
+    for item in iterable:
+        yield item
+
+
+class AsyncLoopContext(LoopContext):
+    _to_iterator = staticmethod(auto_aiter)
+
+    @property
+    async def length(self):
+        if self._length is not None:
+            return self._length
+
+        try:
+            self._length = len(self._iterable)
+        except TypeError:
+            iterable = [x async for x in self._iterator]
+            self._iterator = self._to_iterator(iterable)
+            self._length = len(iterable) + self.index + (self._after is not missing)
+
+        return self._length
+
+    @property
+    async def revindex0(self):
+        return await self.length - self.index
+
+    @property
+    async def revindex(self):
+        return await self.length - self.index0
+
+    async def _peek_next(self):
+        if self._after is not missing:
+            return self._after
+
+        try:
+            self._after = await self._iterator.__anext__()
+        except StopAsyncIteration:
+            self._after = missing
+
+        return self._after
+
+    @property
+    async def last(self):
+        return await self._peek_next() is missing
+
+    @property
+    async def nextitem(self):
+        rv = await self._peek_next()
+
+        if rv is missing:
+            return self._undefined("there is no next item")
+
+        return rv
+
+    def __aiter__(self):
+        return self
+
+    async def __anext__(self):
+        if self._after is not missing:
+            rv = self._after
+            self._after = missing
+        else:
+            rv = await self._iterator.__anext__()
+
+        self.index0 += 1
+        self._before = self._current
+        self._current = rv
+        return rv, self
+
+
+async def make_async_loop_context(iterable, undefined, recurse=None, depth0=0):
+    import warnings
+    warnings.warn(
+        "This template must be recompiled with at least Jinja 2.11, or"
+        " it will fail in 3.0.",
+        DeprecationWarning,
+        stacklevel=2,
+    )
+    return AsyncLoopContext(iterable, undefined, recurse, depth0)
+
+
+patch_all()
diff --git a/src/jinja2/bccache.py b/src/jinja2/bccache.py
new file mode 100644
index 0000000..1a7b5bf
--- /dev/null
+++ b/src/jinja2/bccache.py
@@ -0,0 +1,361 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.bccache
+    ~~~~~~~~~~~~~~
+
+    This module implements the bytecode cache system that Jinja optionally uses.
+    This is useful if you have very complex template situations and
+    the compilation of all those templates slows down your application too
+    much.
+
+    Situations where this is useful are often forking web applications that
+    are initialized on the first request.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+from os import path, listdir
+import os
+import sys
+import stat
+import errno
+import marshal
+import tempfile
+import fnmatch
+from hashlib import sha1
+from jinja2.utils import open_if_exists
+from jinja2._compat import BytesIO, pickle, PY2, text_type
+
+
+# marshal works better on 3.x, one hack less required
+if not PY2:
+    marshal_dump = marshal.dump
+    marshal_load = marshal.load
+else:
+
+    def marshal_dump(code, f):
+        if isinstance(f, file):
+            marshal.dump(code, f)
+        else:
+            f.write(marshal.dumps(code))
+
+    def marshal_load(f):
+        if isinstance(f, file):
+            return marshal.load(f)
+        return marshal.loads(f.read())
+
+
+bc_version = 3
+
+# magic version used to only change with new jinja versions.  With 2.6
+# we change this to also take Python version changes into account.  The
+# reason for this is that Python tends to segfault if fed earlier bytecode
+# versions because someone thought it would be a good idea to reuse opcodes
+# or make Python incompatible with earlier versions.
+bc_magic = 'j2'.encode('ascii') + \
+    pickle.dumps(bc_version, 2) + \
+    pickle.dumps((sys.version_info[0] << 24) | sys.version_info[1])
+
+
+class Bucket(object):
+    """Buckets are used to store the bytecode for one template.  It's created
+    and initialized by the bytecode cache and passed to the loading functions.
+
+    The buckets get an internal checksum from the cache assigned and use this
+    to automatically reject outdated cache material.  Individual bytecode
+    cache subclasses don't have to care about cache invalidation.
+    """
+
+    def __init__(self, environment, key, checksum):
+        self.environment = environment
+        self.key = key
+        self.checksum = checksum
+        self.reset()
+
+    def reset(self):
+        """Resets the bucket (unloads the bytecode)."""
+        self.code = None
+
+    def load_bytecode(self, f):
+        """Loads bytecode from a file or file like object."""
+        # make sure the magic header is correct
+        magic = f.read(len(bc_magic))
+        if magic != bc_magic:
+            self.reset()
+            return
+        # the source code of the file changed, we need to reload
+        checksum = pickle.load(f)
+        if self.checksum != checksum:
+            self.reset()
+            return
+        # if marshal_load fails then we need to reload
+        try:
+            self.code = marshal_load(f)
+        except (EOFError, ValueError, TypeError):
+            self.reset()
+            return
+
+    def write_bytecode(self, f):
+        """Dump the bytecode into the file or file like object passed."""
+        if self.code is None:
+            raise TypeError('can\'t write empty bucket')
+        f.write(bc_magic)
+        pickle.dump(self.checksum, f, 2)
+        marshal_dump(self.code, f)
+
+    def bytecode_from_string(self, string):
+        """Load bytecode from a string."""
+        self.load_bytecode(BytesIO(string))
+
+    def bytecode_to_string(self):
+        """Return the bytecode as string."""
+        out = BytesIO()
+        self.write_bytecode(out)
+        return out.getvalue()
+
+
+class BytecodeCache(object):
+    """To implement your own bytecode cache you have to subclass this class
+    and override :meth:`load_bytecode` and :meth:`dump_bytecode`.  Both of
+    these methods are passed a :class:`~jinja2.bccache.Bucket`.
+
+    A very basic bytecode cache that saves the bytecode on the file system::
+
+        from os import path
+
+        class MyCache(BytecodeCache):
+
+            def __init__(self, directory):
+                self.directory = directory
+
+            def load_bytecode(self, bucket):
+                filename = path.join(self.directory, bucket.key)
+                if path.exists(filename):
+                    with open(filename, 'rb') as f:
+                        bucket.load_bytecode(f)
+
+            def dump_bytecode(self, bucket):
+                filename = path.join(self.directory, bucket.key)
+                with open(filename, 'wb') as f:
+                    bucket.write_bytecode(f)
+
+    A more advanced version of a filesystem based bytecode cache is part of
+    Jinja.
+    """
+
+    def load_bytecode(self, bucket):
+        """Subclasses have to override this method to load bytecode into a
+        bucket.  If they are not able to find code in the cache for the
+        bucket, it must not do anything.
+        """
+        raise NotImplementedError()
+
+    def dump_bytecode(self, bucket):
+        """Subclasses have to override this method to write the bytecode
+        from a bucket back to the cache.  If it unable to do so it must not
+        fail silently but raise an exception.
+        """
+        raise NotImplementedError()
+
+    def clear(self):
+        """Clears the cache.  This method is not used by Jinja but should be
+        implemented to allow applications to clear the bytecode cache used
+        by a particular environment.
+        """
+
+    def get_cache_key(self, name, filename=None):
+        """Returns the unique hash key for this template name."""
+        hash = sha1(name.encode('utf-8'))
+        if filename is not None:
+            filename = '|' + filename
+            if isinstance(filename, text_type):
+                filename = filename.encode('utf-8')
+            hash.update(filename)
+        return hash.hexdigest()
+
+    def get_source_checksum(self, source):
+        """Returns a checksum for the source."""
+        return sha1(source.encode('utf-8')).hexdigest()
+
+    def get_bucket(self, environment, name, filename, source):
+        """Return a cache bucket for the given template.  All arguments are
+        mandatory but filename may be `None`.
+        """
+        key = self.get_cache_key(name, filename)
+        checksum = self.get_source_checksum(source)
+        bucket = Bucket(environment, key, checksum)
+        self.load_bytecode(bucket)
+        return bucket
+
+    def set_bucket(self, bucket):
+        """Put the bucket into the cache."""
+        self.dump_bytecode(bucket)
+
+
+class FileSystemBytecodeCache(BytecodeCache):
+    """A bytecode cache that stores bytecode on the filesystem.  It accepts
+    two arguments: The directory where the cache items are stored and a
+    pattern string that is used to build the filename.
+
+    If no directory is specified a default cache directory is selected.  On
+    Windows the user's temp directory is used, on UNIX systems a directory
+    is created for the user in the system temp directory.
+
+    The pattern can be used to have multiple separate caches operate on the
+    same directory.  The default pattern is ``'__jinja2_%s.cache'``.  ``%s``
+    is replaced with the cache key.
+
+    >>> bcc = FileSystemBytecodeCache('/tmp/jinja_cache', '%s.cache')
+
+    This bytecode cache supports clearing of the cache using the clear method.
+    """
+
+    def __init__(self, directory=None, pattern='__jinja2_%s.cache'):
+        if directory is None:
+            directory = self._get_default_cache_dir()
+        self.directory = directory
+        self.pattern = pattern
+
+    def _get_default_cache_dir(self):
+        def _unsafe_dir():
+            raise RuntimeError('Cannot determine safe temp directory.  You '
+                               'need to explicitly provide one.')
+
+        tmpdir = tempfile.gettempdir()
+
+        # On windows the temporary directory is used specific unless
+        # explicitly forced otherwise.  We can just use that.
+        if os.name == 'nt':
+            return tmpdir
+        if not hasattr(os, 'getuid'):
+            _unsafe_dir()
+
+        dirname = '_jinja2-cache-%d' % os.getuid()
+        actual_dir = os.path.join(tmpdir, dirname)
+
+        try:
+            os.mkdir(actual_dir, stat.S_IRWXU)
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise
+        try:
+            os.chmod(actual_dir, stat.S_IRWXU)
+            actual_dir_stat = os.lstat(actual_dir)
+            if actual_dir_stat.st_uid != os.getuid() \
+               or not stat.S_ISDIR(actual_dir_stat.st_mode) \
+               or stat.S_IMODE(actual_dir_stat.st_mode) != stat.S_IRWXU:
+                _unsafe_dir()
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise
+
+        actual_dir_stat = os.lstat(actual_dir)
+        if actual_dir_stat.st_uid != os.getuid() \
+           or not stat.S_ISDIR(actual_dir_stat.st_mode) \
+           or stat.S_IMODE(actual_dir_stat.st_mode) != stat.S_IRWXU:
+            _unsafe_dir()
+
+        return actual_dir
+
+    def _get_cache_filename(self, bucket):
+        return path.join(self.directory, self.pattern % bucket.key)
+
+    def load_bytecode(self, bucket):
+        f = open_if_exists(self._get_cache_filename(bucket), 'rb')
+        if f is not None:
+            try:
+                bucket.load_bytecode(f)
+            finally:
+                f.close()
+
+    def dump_bytecode(self, bucket):
+        f = open(self._get_cache_filename(bucket), 'wb')
+        try:
+            bucket.write_bytecode(f)
+        finally:
+            f.close()
+
+    def clear(self):
+        # imported lazily here because google app-engine doesn't support
+        # write access on the file system and the function does not exist
+        # normally.
+        from os import remove
+        files = fnmatch.filter(listdir(self.directory), self.pattern % '*')
+        for filename in files:
+            try:
+                remove(path.join(self.directory, filename))
+            except OSError:
+                pass
+
+
+class MemcachedBytecodeCache(BytecodeCache):
+    """This class implements a bytecode cache that uses a memcache cache for
+    storing the information.  It does not enforce a specific memcache library
+    (tummy's memcache or cmemcache) but will accept any class that provides
+    the minimal interface required.
+
+    Libraries compatible with this class:
+
+    -   `cachelib <https://github.com/pallets/cachelib>`_
+    -   `python-memcached <https://pypi.org/project/python-memcached/>`_
+
+    (Unfortunately the django cache interface is not compatible because it
+    does not support storing binary data, only unicode.  You can however pass
+    the underlying cache client to the bytecode cache which is available
+    as `django.core.cache.cache._client`.)
+
+    The minimal interface for the client passed to the constructor is this:
+
+    .. class:: MinimalClientInterface
+
+        .. method:: set(key, value[, timeout])
+
+            Stores the bytecode in the cache.  `value` is a string and
+            `timeout` the timeout of the key.  If timeout is not provided
+            a default timeout or no timeout should be assumed, if it's
+            provided it's an integer with the number of seconds the cache
+            item should exist.
+
+        .. method:: get(key)
+
+            Returns the value for the cache key.  If the item does not
+            exist in the cache the return value must be `None`.
+
+    The other arguments to the constructor are the prefix for all keys that
+    is added before the actual cache key and the timeout for the bytecode in
+    the cache system.  We recommend a high (or no) timeout.
+
+    This bytecode cache does not support clearing of used items in the cache.
+    The clear method is a no-operation function.
+
+    .. versionadded:: 2.7
+       Added support for ignoring memcache errors through the
+       `ignore_memcache_errors` parameter.
+    """
+
+    def __init__(self, client, prefix='jinja2/bytecode/', timeout=None,
+                 ignore_memcache_errors=True):
+        self.client = client
+        self.prefix = prefix
+        self.timeout = timeout
+        self.ignore_memcache_errors = ignore_memcache_errors
+
+    def load_bytecode(self, bucket):
+        try:
+            code = self.client.get(self.prefix + bucket.key)
+        except Exception:
+            if not self.ignore_memcache_errors:
+                raise
+            code = None
+        if code is not None:
+            bucket.bytecode_from_string(code)
+
+    def dump_bytecode(self, bucket):
+        args = (self.prefix + bucket.key, bucket.bytecode_to_string())
+        if self.timeout is not None:
+            args += (self.timeout,)
+        try:
+            self.client.set(*args)
+        except Exception:
+            if not self.ignore_memcache_errors:
+                raise
diff --git a/src/jinja2/compiler.py b/src/jinja2/compiler.py
new file mode 100644
index 0000000..addf71e
--- /dev/null
+++ b/src/jinja2/compiler.py
@@ -0,0 +1,1772 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.compiler
+    ~~~~~~~~~~~~~~~
+
+    Compiles nodes into python code.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+from collections import namedtuple
+from itertools import chain
+from keyword import iskeyword as is_python_keyword
+from functools import update_wrapper
+from jinja2 import nodes
+from jinja2.nodes import EvalContext
+from jinja2.visitor import NodeVisitor
+from jinja2.optimizer import Optimizer
+from jinja2.exceptions import TemplateAssertionError
+from jinja2.utils import Markup, concat, escape
+from jinja2._compat import range_type, text_type, string_types, \
+     iteritems, NativeStringIO, imap, izip
+from jinja2.idtracking import Symbols, VAR_LOAD_PARAMETER, \
+     VAR_LOAD_RESOLVE, VAR_LOAD_ALIAS, VAR_LOAD_UNDEFINED
+
+
+operators = {
+    'eq':       '==',
+    'ne':       '!=',
+    'gt':       '>',
+    'gteq':     '>=',
+    'lt':       '<',
+    'lteq':     '<=',
+    'in':       'in',
+    'notin':    'not in'
+}
+
+# what method to iterate over items do we want to use for dict iteration
+# in generated code?  on 2.x let's go with iteritems, on 3.x with items
+if hasattr(dict, 'iteritems'):
+    dict_item_iter = 'iteritems'
+else:
+    dict_item_iter = 'items'
+
+code_features = ['division']
+
+# does this python version support generator stops? (PEP 0479)
+try:
+    exec('from __future__ import generator_stop')
+    code_features.append('generator_stop')
+except SyntaxError:
+    pass
+
+# does this python version support yield from?
+try:
+    exec('def f(): yield from x()')
+except SyntaxError:
+    supports_yield_from = False
+else:
+    supports_yield_from = True
+
+
+def optimizeconst(f):
+    def new_func(self, node, frame, **kwargs):
+        # Only optimize if the frame is not volatile
+        if self.optimized and not frame.eval_ctx.volatile:
+            new_node = self.optimizer.visit(node, frame.eval_ctx)
+            if new_node != node:
+                return self.visit(new_node, frame)
+        return f(self, node, frame, **kwargs)
+    return update_wrapper(new_func, f)
+
+
+def generate(node, environment, name, filename, stream=None,
+             defer_init=False, optimized=True):
+    """Generate the python source for a node tree."""
+    if not isinstance(node, nodes.Template):
+        raise TypeError('Can\'t compile non template nodes')
+    generator = environment.code_generator_class(environment, name, filename,
+                                                 stream, defer_init,
+                                                 optimized)
+    generator.visit(node)
+    if stream is None:
+        return generator.stream.getvalue()
+
+
+def has_safe_repr(value):
+    """Does the node have a safe representation?"""
+    if value is None or value is NotImplemented or value is Ellipsis:
+        return True
+    if type(value) in (bool, int, float, complex, range_type, Markup) + string_types:
+        return True
+    if type(value) in (tuple, list, set, frozenset):
+        for item in value:
+            if not has_safe_repr(item):
+                return False
+        return True
+    elif type(value) is dict:
+        for key, value in iteritems(value):
+            if not has_safe_repr(key):
+                return False
+            if not has_safe_repr(value):
+                return False
+        return True
+    return False
+
+
+def find_undeclared(nodes, names):
+    """Check if the names passed are accessed undeclared.  The return value
+    is a set of all the undeclared names from the sequence of names found.
+    """
+    visitor = UndeclaredNameVisitor(names)
+    try:
+        for node in nodes:
+            visitor.visit(node)
+    except VisitorExit:
+        pass
+    return visitor.undeclared
+
+
+class MacroRef(object):
+
+    def __init__(self, node):
+        self.node = node
+        self.accesses_caller = False
+        self.accesses_kwargs = False
+        self.accesses_varargs = False
+
+
+class Frame(object):
+    """Holds compile time information for us."""
+
+    def __init__(self, eval_ctx, parent=None, level=None):
+        self.eval_ctx = eval_ctx
+        self.symbols = Symbols(parent and parent.symbols or None,
+                               level=level)
+
+        # a toplevel frame is the root + soft frames such as if conditions.
+        self.toplevel = False
+
+        # the root frame is basically just the outermost frame, so no if
+        # conditions.  This information is used to optimize inheritance
+        # situations.
+        self.rootlevel = False
+
+        # in some dynamic inheritance situations the compiler needs to add
+        # write tests around output statements.
+        self.require_output_check = parent and parent.require_output_check
+
+        # inside some tags we are using a buffer rather than yield statements.
+        # this for example affects {% filter %} or {% macro %}.  If a frame
+        # is buffered this variable points to the name of the list used as
+        # buffer.
+        self.buffer = None
+
+        # the name of the block we're in, otherwise None.
+        self.block = parent and parent.block or None
+
+        # the parent of this frame
+        self.parent = parent
+
+        if parent is not None:
+            self.buffer = parent.buffer
+
+    def copy(self):
+        """Create a copy of the current one."""
+        rv = object.__new__(self.__class__)
+        rv.__dict__.update(self.__dict__)
+        rv.symbols = self.symbols.copy()
+        return rv
+
+    def inner(self, isolated=False):
+        """Return an inner frame."""
+        if isolated:
+            return Frame(self.eval_ctx, level=self.symbols.level + 1)
+        return Frame(self.eval_ctx, self)
+
+    def soft(self):
+        """Return a soft frame.  A soft frame may not be modified as
+        standalone thing as it shares the resources with the frame it
+        was created of, but it's not a rootlevel frame any longer.
+
+        This is only used to implement if-statements.
+        """
+        rv = self.copy()
+        rv.rootlevel = False
+        return rv
+
+    __copy__ = copy
+
+
+class VisitorExit(RuntimeError):
+    """Exception used by the `UndeclaredNameVisitor` to signal a stop."""
+
+
+class DependencyFinderVisitor(NodeVisitor):
+    """A visitor that collects filter and test calls."""
+
+    def __init__(self):
+        self.filters = set()
+        self.tests = set()
+
+    def visit_Filter(self, node):
+        self.generic_visit(node)
+        self.filters.add(node.name)
+
+    def visit_Test(self, node):
+        self.generic_visit(node)
+        self.tests.add(node.name)
+
+    def visit_Block(self, node):
+        """Stop visiting at blocks."""
+
+
+class UndeclaredNameVisitor(NodeVisitor):
+    """A visitor that checks if a name is accessed without being
+    declared.  This is different from the frame visitor as it will
+    not stop at closure frames.
+    """
+
+    def __init__(self, names):
+        self.names = set(names)
+        self.undeclared = set()
+
+    def visit_Name(self, node):
+        if node.ctx == 'load' and node.name in self.names:
+            self.undeclared.add(node.name)
+            if self.undeclared == self.names:
+                raise VisitorExit()
+        else:
+            self.names.discard(node.name)
+
+    def visit_Block(self, node):
+        """Stop visiting a blocks."""
+
+
+class CompilerExit(Exception):
+    """Raised if the compiler encountered a situation where it just
+    doesn't make sense to further process the code.  Any block that
+    raises such an exception is not further processed.
+    """
+
+
+class CodeGenerator(NodeVisitor):
+
+    def __init__(self, environment, name, filename, stream=None,
+                 defer_init=False, optimized=True):
+        if stream is None:
+            stream = NativeStringIO()
+        self.environment = environment
+        self.name = name
+        self.filename = filename
+        self.stream = stream
+        self.created_block_context = False
+        self.defer_init = defer_init
+        self.optimized = optimized
+        if optimized:
+            self.optimizer = Optimizer(environment)
+
+        # aliases for imports
+        self.import_aliases = {}
+
+        # a registry for all blocks.  Because blocks are moved out
+        # into the global python scope they are registered here
+        self.blocks = {}
+
+        # the number of extends statements so far
+        self.extends_so_far = 0
+
+        # some templates have a rootlevel extends.  In this case we
+        # can safely assume that we're a child template and do some
+        # more optimizations.
+        self.has_known_extends = False
+
+        # the current line number
+        self.code_lineno = 1
+
+        # registry of all filters and tests (global, not block local)
+        self.tests = {}
+        self.filters = {}
+
+        # the debug information
+        self.debug_info = []
+        self._write_debug_info = None
+
+        # the number of new lines before the next write()
+        self._new_lines = 0
+
+        # the line number of the last written statement
+        self._last_line = 0
+
+        # true if nothing was written so far.
+        self._first_write = True
+
+        # used by the `temporary_identifier` method to get new
+        # unique, temporary identifier
+        self._last_identifier = 0
+
+        # the current indentation
+        self._indentation = 0
+
+        # Tracks toplevel assignments
+        self._assign_stack = []
+
+        # Tracks parameter definition blocks
+        self._param_def_block = []
+
+        # Tracks the current context.
+        self._context_reference_stack = ['context']
+
+    # -- Various compilation helpers
+
+    def fail(self, msg, lineno):
+        """Fail with a :exc:`TemplateAssertionError`."""
+        raise TemplateAssertionError(msg, lineno, self.name, self.filename)
+
+    def temporary_identifier(self):
+        """Get a new unique identifier."""
+        self._last_identifier += 1
+        return 't_%d' % self._last_identifier
+
+    def buffer(self, frame):
+        """Enable buffering for the frame from that point onwards."""
+        frame.buffer = self.temporary_identifier()
+        self.writeline('%s = []' % frame.buffer)
+
+    def return_buffer_contents(self, frame, force_unescaped=False):
+        """Return the buffer contents of the frame."""
+        if not force_unescaped:
+            if frame.eval_ctx.volatile:
+                self.writeline('if context.eval_ctx.autoescape:')
+                self.indent()
+                self.writeline('return Markup(concat(%s))' % frame.buffer)
+                self.outdent()
+                self.writeline('else:')
+                self.indent()
+                self.writeline('return concat(%s)' % frame.buffer)
+                self.outdent()
+                return
+            elif frame.eval_ctx.autoescape:
+                self.writeline('return Markup(concat(%s))' % frame.buffer)
+                return
+        self.writeline('return concat(%s)' % frame.buffer)
+
+    def indent(self):
+        """Indent by one."""
+        self._indentation += 1
+
+    def outdent(self, step=1):
+        """Outdent by step."""
+        self._indentation -= step
+
+    def start_write(self, frame, node=None):
+        """Yield or write into the frame buffer."""
+        if frame.buffer is None:
+            self.writeline('yield ', node)
+        else:
+            self.writeline('%s.append(' % frame.buffer, node)
+
+    def end_write(self, frame):
+        """End the writing process started by `start_write`."""
+        if frame.buffer is not None:
+            self.write(')')
+
+    def simple_write(self, s, frame, node=None):
+        """Simple shortcut for start_write + write + end_write."""
+        self.start_write(frame, node)
+        self.write(s)
+        self.end_write(frame)
+
+    def blockvisit(self, nodes, frame):
+        """Visit a list of nodes as block in a frame.  If the current frame
+        is no buffer a dummy ``if 0: yield None`` is written automatically.
+        """
+        try:
+            self.writeline('pass')
+            for node in nodes:
+                self.visit(node, frame)
+        except CompilerExit:
+            pass
+
+    def write(self, x):
+        """Write a string into the output stream."""
+        if self._new_lines:
+            if not self._first_write:
+                self.stream.write('\n' * self._new_lines)
+                self.code_lineno += self._new_lines
+                if self._write_debug_info is not None:
+                    self.debug_info.append((self._write_debug_info,
+                                            self.code_lineno))
+                    self._write_debug_info = None
+            self._first_write = False
+            self.stream.write('    ' * self._indentation)
+            self._new_lines = 0
+        self.stream.write(x)
+
+    def writeline(self, x, node=None, extra=0):
+        """Combination of newline and write."""
+        self.newline(node, extra)
+        self.write(x)
+
+    def newline(self, node=None, extra=0):
+        """Add one or more newlines before the next write."""
+        self._new_lines = max(self._new_lines, 1 + extra)
+        if node is not None and node.lineno != self._last_line:
+            self._write_debug_info = node.lineno
+            self._last_line = node.lineno
+
+    def signature(self, node, frame, extra_kwargs=None):
+        """Writes a function call to the stream for the current node.
+        A leading comma is added automatically.  The extra keyword
+        arguments may not include python keywords otherwise a syntax
+        error could occur.  The extra keyword arguments should be given
+        as python dict.
+        """
+        # if any of the given keyword arguments is a python keyword
+        # we have to make sure that no invalid call is created.
+        kwarg_workaround = False
+        for kwarg in chain((x.key for x in node.kwargs), extra_kwargs or ()):
+            if is_python_keyword(kwarg):
+                kwarg_workaround = True
+                break
+
+        for arg in node.args:
+            self.write(', ')
+            self.visit(arg, frame)
+
+        if not kwarg_workaround:
+            for kwarg in node.kwargs:
+                self.write(', ')
+                self.visit(kwarg, frame)
+            if extra_kwargs is not None:
+                for key, value in iteritems(extra_kwargs):
+                    self.write(', %s=%s' % (key, value))
+        if node.dyn_args:
+            self.write(', *')
+            self.visit(node.dyn_args, frame)
+
+        if kwarg_workaround:
+            if node.dyn_kwargs is not None:
+                self.write(', **dict({')
+            else:
+                self.write(', **{')
+            for kwarg in node.kwargs:
+                self.write('%r: ' % kwarg.key)
+                self.visit(kwarg.value, frame)
+                self.write(', ')
+            if extra_kwargs is not None:
+                for key, value in iteritems(extra_kwargs):
+                    self.write('%r: %s, ' % (key, value))
+            if node.dyn_kwargs is not None:
+                self.write('}, **')
+                self.visit(node.dyn_kwargs, frame)
+                self.write(')')
+            else:
+                self.write('}')
+
+        elif node.dyn_kwargs is not None:
+            self.write(', **')
+            self.visit(node.dyn_kwargs, frame)
+
+    def pull_dependencies(self, nodes):
+        """Pull all the dependencies."""
+        visitor = DependencyFinderVisitor()
+        for node in nodes:
+            visitor.visit(node)
+        for dependency in 'filters', 'tests':
+            mapping = getattr(self, dependency)
+            for name in getattr(visitor, dependency):
+                if name not in mapping:
+                    mapping[name] = self.temporary_identifier()
+                self.writeline('%s = environment.%s[%r]' %
+                               (mapping[name], dependency, name))
+
+    def enter_frame(self, frame):
+        undefs = []
+        for target, (action, param) in iteritems(frame.symbols.loads):
+            if action == VAR_LOAD_PARAMETER:
+                pass
+            elif action == VAR_LOAD_RESOLVE:
+                self.writeline('%s = %s(%r)' %
+                               (target, self.get_resolve_func(), param))
+            elif action == VAR_LOAD_ALIAS:
+                self.writeline('%s = %s' % (target, param))
+            elif action == VAR_LOAD_UNDEFINED:
+                undefs.append(target)
+            else:
+                raise NotImplementedError('unknown load instruction')
+        if undefs:
+            self.writeline('%s = missing' % ' = '.join(undefs))
+
+    def leave_frame(self, frame, with_python_scope=False):
+        if not with_python_scope:
+            undefs = []
+            for target, _ in iteritems(frame.symbols.loads):
+                undefs.append(target)
+            if undefs:
+                self.writeline('%s = missing' % ' = '.join(undefs))
+
+    def func(self, name):
+        if self.environment.is_async:
+            return 'async def %s' % name
+        return 'def %s' % name
+
+    def macro_body(self, node, frame):
+        """Dump the function def of a macro or call block."""
+        frame = frame.inner()
+        frame.symbols.analyze_node(node)
+        macro_ref = MacroRef(node)
+
+        explicit_caller = None
+        skip_special_params = set()
+        args = []
+        for idx, arg in enumerate(node.args):
+            if arg.name == 'caller':
+                explicit_caller = idx
+            if arg.name in ('kwargs', 'varargs'):
+                skip_special_params.add(arg.name)
+            args.append(frame.symbols.ref(arg.name))
+
+        undeclared = find_undeclared(node.body, ('caller', 'kwargs', 'varargs'))
+
+        if 'caller' in undeclared:
+            # In older Jinja versions there was a bug that allowed caller
+            # to retain the special behavior even if it was mentioned in
+            # the argument list.  However thankfully this was only really
+            # working if it was the last argument.  So we are explicitly
+            # checking this now and error out if it is anywhere else in
+            # the argument list.
+            if explicit_caller is not None:
+                try:
+                    node.defaults[explicit_caller - len(node.args)]
+                except IndexError:
+                    self.fail('When defining macros or call blocks the '
+                              'special "caller" argument must be omitted '
+                              'or be given a default.', node.lineno)
+            else:
+                args.append(frame.symbols.declare_parameter('caller'))
+            macro_ref.accesses_caller = True
+        if 'kwargs' in undeclared and not 'kwargs' in skip_special_params:
+            args.append(frame.symbols.declare_parameter('kwargs'))
+            macro_ref.accesses_kwargs = True
+        if 'varargs' in undeclared and not 'varargs' in skip_special_params:
+            args.append(frame.symbols.declare_parameter('varargs'))
+            macro_ref.accesses_varargs = True
+
+        # macros are delayed, they never require output checks
+        frame.require_output_check = False
+        frame.symbols.analyze_node(node)
+        self.writeline('%s(%s):' % (self.func('macro'), ', '.join(args)), node)
+        self.indent()
+
+        self.buffer(frame)
+        self.enter_frame(frame)
+
+        self.push_parameter_definitions(frame)
+        for idx, arg in enumerate(node.args):
+            ref = frame.symbols.ref(arg.name)
+            self.writeline('if %s is missing:' % ref)
+            self.indent()
+            try:
+                default = node.defaults[idx - len(node.args)]
+            except IndexError:
+                self.writeline('%s = undefined(%r, name=%r)' % (
+                    ref,
+                    'parameter %r was not provided' % arg.name,
+                    arg.name))
+            else:
+                self.writeline('%s = ' % ref)
+                self.visit(default, frame)
+            self.mark_parameter_stored(ref)
+            self.outdent()
+        self.pop_parameter_definitions()
+
+        self.blockvisit(node.body, frame)
+        self.return_buffer_contents(frame, force_unescaped=True)
+        self.leave_frame(frame, with_python_scope=True)
+        self.outdent()
+
+        return frame, macro_ref
+
+    def macro_def(self, macro_ref, frame):
+        """Dump the macro definition for the def created by macro_body."""
+        arg_tuple = ', '.join(repr(x.name) for x in macro_ref.node.args)
+        name = getattr(macro_ref.node, 'name', None)
+        if len(macro_ref.node.args) == 1:
+            arg_tuple += ','
+        self.write('Macro(environment, macro, %r, (%s), %r, %r, %r, '
+                   'context.eval_ctx.autoescape)' %
+                   (name, arg_tuple, macro_ref.accesses_kwargs,
+                    macro_ref.accesses_varargs, macro_ref.accesses_caller))
+
+    def position(self, node):
+        """Return a human readable position for the node."""
+        rv = 'line %d' % node.lineno
+        if self.name is not None:
+            rv += ' in ' + repr(self.name)
+        return rv
+
+    def dump_local_context(self, frame):
+        return '{%s}' % ', '.join(
+            '%r: %s' % (name, target) for name, target
+            in iteritems(frame.symbols.dump_stores()))
+
+    def write_commons(self):
+        """Writes a common preamble that is used by root and block functions.
+        Primarily this sets up common local helpers and enforces a generator
+        through a dead branch.
+        """
+        self.writeline('resolve = context.resolve_or_missing')
+        self.writeline('undefined = environment.undefined')
+        # always use the standard Undefined class for the implicit else of
+        # conditional expressions
+        self.writeline('cond_expr_undefined = Undefined')
+        self.writeline('if 0: yield None')
+
+    def push_parameter_definitions(self, frame):
+        """Pushes all parameter targets from the given frame into a local
+        stack that permits tracking of yet to be assigned parameters.  In
+        particular this enables the optimization from `visit_Name` to skip
+        undefined expressions for parameters in macros as macros can reference
+        otherwise unbound parameters.
+        """
+        self._param_def_block.append(frame.symbols.dump_param_targets())
+
+    def pop_parameter_definitions(self):
+        """Pops the current parameter definitions set."""
+        self._param_def_block.pop()
+
+    def mark_parameter_stored(self, target):
+        """Marks a parameter in the current parameter definitions as stored.
+        This will skip the enforced undefined checks.
+        """
+        if self._param_def_block:
+            self._param_def_block[-1].discard(target)
+
+    def push_context_reference(self, target):
+        self._context_reference_stack.append(target)
+
+    def pop_context_reference(self):
+        self._context_reference_stack.pop()
+
+    def get_context_ref(self):
+        return self._context_reference_stack[-1]
+
+    def get_resolve_func(self):
+        target = self._context_reference_stack[-1]
+        if target == 'context':
+            return 'resolve'
+        return '%s.resolve' % target
+
+    def derive_context(self, frame):
+        return '%s.derived(%s)' % (
+            self.get_context_ref(),
+            self.dump_local_context(frame),
+        )
+
+    def parameter_is_undeclared(self, target):
+        """Checks if a given target is an undeclared parameter."""
+        if not self._param_def_block:
+            return False
+        return target in self._param_def_block[-1]
+
+    def push_assign_tracking(self):
+        """Pushes a new layer for assignment tracking."""
+        self._assign_stack.append(set())
+
+    def pop_assign_tracking(self, frame):
+        """Pops the topmost level for assignment tracking and updates the
+        context variables if necessary.
+        """
+        vars = self._assign_stack.pop()
+        if not frame.toplevel or not vars:
+            return
+        public_names = [x for x in vars if x[:1] != '_']
+        if len(vars) == 1:
+            name = next(iter(vars))
+            ref = frame.symbols.ref(name)
+            self.writeline('context.vars[%r] = %s' % (name, ref))
+        else:
+            self.writeline('context.vars.update({')
+            for idx, name in enumerate(vars):
+                if idx:
+                    self.write(', ')
+                ref = frame.symbols.ref(name)
+                self.write('%r: %s' % (name, ref))
+            self.write('})')
+        if public_names:
+            if len(public_names) == 1:
+                self.writeline('context.exported_vars.add(%r)' %
+                               public_names[0])
+            else:
+                self.writeline('context.exported_vars.update((%s))' %
+                               ', '.join(imap(repr, public_names)))
+
+    # -- Statement Visitors
+
+    def visit_Template(self, node, frame=None):
+        assert frame is None, 'no root frame allowed'
+        eval_ctx = EvalContext(self.environment, self.name)
+
+        from jinja2.runtime import __all__ as exported
+        self.writeline('from __future__ import %s' % ', '.join(code_features))
+        self.writeline('from jinja2.runtime import ' + ', '.join(exported))
+
+        if self.environment.is_async:
+            self.writeline('from jinja2.asyncsupport import auto_await, '
+                           'auto_aiter, AsyncLoopContext')
+
+        # if we want a deferred initialization we cannot move the
+        # environment into a local name
+        envenv = not self.defer_init and ', environment=environment' or ''
+
+        # do we have an extends tag at all?  If not, we can save some
+        # overhead by just not processing any inheritance code.
+        have_extends = node.find(nodes.Extends) is not None
+
+        # find all blocks
+        for block in node.find_all(nodes.Block):
+            if block.name in self.blocks:
+                self.fail('block %r defined twice' % block.name, block.lineno)
+            self.blocks[block.name] = block
+
+        # find all imports and import them
+        for import_ in node.find_all(nodes.ImportedName):
+            if import_.importname not in self.import_aliases:
+                imp = import_.importname
+                self.import_aliases[imp] = alias = self.temporary_identifier()
+                if '.' in imp:
+                    module, obj = imp.rsplit('.', 1)
+                    self.writeline('from %s import %s as %s' %
+                                   (module, obj, alias))
+                else:
+                    self.writeline('import %s as %s' % (imp, alias))
+
+        # add the load name
+        self.writeline('name = %r' % self.name)
+
+        # generate the root render function.
+        self.writeline('%s(context, missing=missing%s):' %
+                       (self.func('root'), envenv), extra=1)
+        self.indent()
+        self.write_commons()
+
+        # process the root
+        frame = Frame(eval_ctx)
+        if 'self' in find_undeclared(node.body, ('self',)):
+            ref = frame.symbols.declare_parameter('self')
+            self.writeline('%s = TemplateReference(context)' % ref)
+        frame.symbols.analyze_node(node)
+        frame.toplevel = frame.rootlevel = True
+        frame.require_output_check = have_extends and not self.has_known_extends
+        if have_extends:
+            self.writeline('parent_template = None')
+        self.enter_frame(frame)
+        self.pull_dependencies(node.body)
+        self.blockvisit(node.body, frame)
+        self.leave_frame(frame, with_python_scope=True)
+        self.outdent()
+
+        # make sure that the parent root is called.
+        if have_extends:
+            if not self.has_known_extends:
+                self.indent()
+                self.writeline('if parent_template is not None:')
+            self.indent()
+            if supports_yield_from and not self.environment.is_async:
+                self.writeline('yield from parent_template.'
+                               'root_render_func(context)')
+            else:
+                self.writeline('%sfor event in parent_template.'
+                               'root_render_func(context):' %
+                               (self.environment.is_async and 'async ' or ''))
+                self.indent()
+                self.writeline('yield event')
+                self.outdent()
+            self.outdent(1 + (not self.has_known_extends))
+
+        # at this point we now have the blocks collected and can visit them too.
+        for name, block in iteritems(self.blocks):
+            self.writeline('%s(context, missing=missing%s):' %
+                           (self.func('block_' + name), envenv),
+                           block, 1)
+            self.indent()
+            self.write_commons()
+            # It's important that we do not make this frame a child of the
+            # toplevel template.  This would cause a variety of
+            # interesting issues with identifier tracking.
+            block_frame = Frame(eval_ctx)
+            undeclared = find_undeclared(block.body, ('self', 'super'))
+            if 'self' in undeclared:
+                ref = block_frame.symbols.declare_parameter('self')
+                self.writeline('%s = TemplateReference(context)' % ref)
+            if 'super' in undeclared:
+                ref = block_frame.symbols.declare_parameter('super')
+                self.writeline('%s = context.super(%r, '
+                               'block_%s)' % (ref, name, name))
+            block_frame.symbols.analyze_node(block)
+            block_frame.block = name
+            self.enter_frame(block_frame)
+            self.pull_dependencies(block.body)
+            self.blockvisit(block.body, block_frame)
+            self.leave_frame(block_frame, with_python_scope=True)
+            self.outdent()
+
+        self.writeline('blocks = {%s}' % ', '.join('%r: block_%s' % (x, x)
+                                                   for x in self.blocks),
+                       extra=1)
+
+        # add a function that returns the debug info
+        self.writeline('debug_info = %r' % '&'.join('%s=%s' % x for x
+                                                    in self.debug_info))
+
+    def visit_Block(self, node, frame):
+        """Call a block and register it for the template."""
+        level = 0
+        if frame.toplevel:
+            # if we know that we are a child template, there is no need to
+            # check if we are one
+            if self.has_known_extends:
+                return
+            if self.extends_so_far > 0:
+                self.writeline('if parent_template is None:')
+                self.indent()
+                level += 1
+
+        if node.scoped:
+            context = self.derive_context(frame)
+        else:
+            context = self.get_context_ref()
+
+        if supports_yield_from and not self.environment.is_async and \
+           frame.buffer is None:
+            self.writeline('yield from context.blocks[%r][0](%s)' % (
+                           node.name, context), node)
+        else:
+            loop = self.environment.is_async and 'async for' or 'for'
+            self.writeline('%s event in context.blocks[%r][0](%s):' % (
+                           loop, node.name, context), node)
+            self.indent()
+            self.simple_write('event', frame)
+            self.outdent()
+
+        self.outdent(level)
+
+    def visit_Extends(self, node, frame):
+        """Calls the extender."""
+        if not frame.toplevel:
+            self.fail('cannot use extend from a non top-level scope',
+                      node.lineno)
+
+        # if the number of extends statements in general is zero so
+        # far, we don't have to add a check if something extended
+        # the template before this one.
+        if self.extends_so_far > 0:
+
+            # if we have a known extends we just add a template runtime
+            # error into the generated code.  We could catch that at compile
+            # time too, but i welcome it not to confuse users by throwing the
+            # same error at different times just "because we can".
+            if not self.has_known_extends:
+                self.writeline('if parent_template is not None:')
+                self.indent()
+            self.writeline('raise TemplateRuntimeError(%r)' %
+                           'extended multiple times')
+
+            # if we have a known extends already we don't need that code here
+            # as we know that the template execution will end here.
+            if self.has_known_extends:
+                raise CompilerExit()
+            else:
+                self.outdent()
+
+        self.writeline('parent_template = environment.get_template(', node)
+        self.visit(node.template, frame)
+        self.write(', %r)' % self.name)
+        self.writeline('for name, parent_block in parent_template.'
+                       'blocks.%s():' % dict_item_iter)
+        self.indent()
+        self.writeline('context.blocks.setdefault(name, []).'
+                       'append(parent_block)')
+        self.outdent()
+
+        # if this extends statement was in the root level we can take
+        # advantage of that information and simplify the generated code
+        # in the top level from this point onwards
+        if frame.rootlevel:
+            self.has_known_extends = True
+
+        # and now we have one more
+        self.extends_so_far += 1
+
+    def visit_Include(self, node, frame):
+        """Handles includes."""
+        if node.ignore_missing:
+            self.writeline('try:')
+            self.indent()
+
+        func_name = 'get_or_select_template'
+        if isinstance(node.template, nodes.Const):
+            if isinstance(node.template.value, string_types):
+                func_name = 'get_template'
+            elif isinstance(node.template.value, (tuple, list)):
+                func_name = 'select_template'
+        elif isinstance(node.template, (nodes.Tuple, nodes.List)):
+            func_name = 'select_template'
+
+        self.writeline('template = environment.%s(' % func_name, node)
+        self.visit(node.template, frame)
+        self.write(', %r)' % self.name)
+        if node.ignore_missing:
+            self.outdent()
+            self.writeline('except TemplateNotFound:')
+            self.indent()
+            self.writeline('pass')
+            self.outdent()
+            self.writeline('else:')
+            self.indent()
+
+        skip_event_yield = False
+        if node.with_context:
+            loop = self.environment.is_async and 'async for' or 'for'
+            self.writeline('%s event in template.root_render_func('
+                           'template.new_context(context.get_all(), True, '
+                           '%s)):' % (loop, self.dump_local_context(frame)))
+        elif self.environment.is_async:
+            self.writeline('for event in (await '
+                           'template._get_default_module_async())'
+                           '._body_stream:')
+        else:
+            if supports_yield_from:
+                self.writeline('yield from template._get_default_module()'
+                               '._body_stream')
+                skip_event_yield = True
+            else:
+                self.writeline('for event in template._get_default_module()'
+                               '._body_stream:')
+
+        if not skip_event_yield:
+            self.indent()
+            self.simple_write('event', frame)
+            self.outdent()
+
+        if node.ignore_missing:
+            self.outdent()
+
+    def visit_Import(self, node, frame):
+        """Visit regular imports."""
+        self.writeline('%s = ' % frame.symbols.ref(node.target), node)
+        if frame.toplevel:
+            self.write('context.vars[%r] = ' % node.target)
+        if self.environment.is_async:
+            self.write('await ')
+        self.write('environment.get_template(')
+        self.visit(node.template, frame)
+        self.write(', %r).' % self.name)
+        if node.with_context:
+            self.write('make_module%s(context.get_all(), True, %s)'
+                       % (self.environment.is_async and '_async' or '',
+                          self.dump_local_context(frame)))
+        elif self.environment.is_async:
+            self.write('_get_default_module_async()')
+        else:
+            self.write('_get_default_module()')
+        if frame.toplevel and not node.target.startswith('_'):
+            self.writeline('context.exported_vars.discard(%r)' % node.target)
+
+    def visit_FromImport(self, node, frame):
+        """Visit named imports."""
+        self.newline(node)
+        self.write('included_template = %senvironment.get_template('
+                   % (self.environment.is_async and 'await ' or ''))
+        self.visit(node.template, frame)
+        self.write(', %r).' % self.name)
+        if node.with_context:
+            self.write('make_module%s(context.get_all(), True, %s)'
+                       % (self.environment.is_async and '_async' or '',
+                          self.dump_local_context(frame)))
+        elif self.environment.is_async:
+            self.write('_get_default_module_async()')
+        else:
+            self.write('_get_default_module()')
+
+        var_names = []
+        discarded_names = []
+        for name in node.names:
+            if isinstance(name, tuple):
+                name, alias = name
+            else:
+                alias = name
+            self.writeline('%s = getattr(included_template, '
+                           '%r, missing)' % (frame.symbols.ref(alias), name))
+            self.writeline('if %s is missing:' % frame.symbols.ref(alias))
+            self.indent()
+            self.writeline('%s = undefined(%r %% '
+                           'included_template.__name__, '
+                           'name=%r)' %
+                           (frame.symbols.ref(alias),
+                            'the template %%r (imported on %s) does '
+                            'not export the requested name %s' % (
+                                self.position(node),
+                                repr(name)
+                           ), name))
+            self.outdent()
+            if frame.toplevel:
+                var_names.append(alias)
+                if not alias.startswith('_'):
+                    discarded_names.append(alias)
+
+        if var_names:
+            if len(var_names) == 1:
+                name = var_names[0]
+                self.writeline('context.vars[%r] = %s' %
+                               (name, frame.symbols.ref(name)))
+            else:
+                self.writeline('context.vars.update({%s})' % ', '.join(
+                    '%r: %s' % (name, frame.symbols.ref(name)) for name in var_names
+                ))
+        if discarded_names:
+            if len(discarded_names) == 1:
+                self.writeline('context.exported_vars.discard(%r)' %
+                               discarded_names[0])
+            else:
+                self.writeline('context.exported_vars.difference_'
+                               'update((%s))' % ', '.join(imap(repr, discarded_names)))
+
+    def visit_For(self, node, frame):
+        loop_frame = frame.inner()
+        test_frame = frame.inner()
+        else_frame = frame.inner()
+
+        # try to figure out if we have an extended loop.  An extended loop
+        # is necessary if the loop is in recursive mode if the special loop
+        # variable is accessed in the body.
+        extended_loop = node.recursive or 'loop' in \
+                        find_undeclared(node.iter_child_nodes(
+                            only=('body',)), ('loop',))
+
+        loop_ref = None
+        if extended_loop:
+            loop_ref = loop_frame.symbols.declare_parameter('loop')
+
+        loop_frame.symbols.analyze_node(node, for_branch='body')
+        if node.else_:
+            else_frame.symbols.analyze_node(node, for_branch='else')
+
+        if node.test:
+            loop_filter_func = self.temporary_identifier()
+            test_frame.symbols.analyze_node(node, for_branch='test')
+            self.writeline('%s(fiter):' % self.func(loop_filter_func), node.test)
+            self.indent()
+            self.enter_frame(test_frame)
+            self.writeline(self.environment.is_async and 'async for ' or 'for ')
+            self.visit(node.target, loop_frame)
+            self.write(' in ')
+            self.write(self.environment.is_async and 'auto_aiter(fiter)' or 'fiter')
+            self.write(':')
+            self.indent()
+            self.writeline('if ', node.test)
+            self.visit(node.test, test_frame)
+            self.write(':')
+            self.indent()
+            self.writeline('yield ')
+            self.visit(node.target, loop_frame)
+            self.outdent(3)
+            self.leave_frame(test_frame, with_python_scope=True)
+
+        # if we don't have an recursive loop we have to find the shadowed
+        # variables at that point.  Because loops can be nested but the loop
+        # variable is a special one we have to enforce aliasing for it.
+        if node.recursive:
+            self.writeline('%s(reciter, loop_render_func, depth=0):' %
+                           self.func('loop'), node)
+            self.indent()
+            self.buffer(loop_frame)
+
+            # Use the same buffer for the else frame
+            else_frame.buffer = loop_frame.buffer
+
+        # make sure the loop variable is a special one and raise a template
+        # assertion error if a loop tries to write to loop
+        if extended_loop:
+            self.writeline('%s = missing' % loop_ref)
+
+        for name in node.find_all(nodes.Name):
+            if name.ctx == 'store' and name.name == 'loop':
+                self.fail('Can\'t assign to special loop variable '
+                          'in for-loop target', name.lineno)
+
+        if node.else_:
+            iteration_indicator = self.temporary_identifier()
+            self.writeline('%s = 1' % iteration_indicator)
+
+        self.writeline(self.environment.is_async and 'async for ' or 'for ', node)
+        self.visit(node.target, loop_frame)
+        if extended_loop:
+            if self.environment.is_async:
+                self.write(', %s in AsyncLoopContext(' % loop_ref)
+            else:
+                self.write(', %s in LoopContext(' % loop_ref)
+        else:
+            self.write(' in ')
+
+        if node.test:
+            self.write('%s(' % loop_filter_func)
+        if node.recursive:
+            self.write('reciter')
+        else:
+            if self.environment.is_async and not extended_loop:
+                self.write('auto_aiter(')
+            self.visit(node.iter, frame)
+            if self.environment.is_async and not extended_loop:
+                self.write(')')
+        if node.test:
+            self.write(')')
+
+        if node.recursive:
+            self.write(', undefined, loop_render_func, depth):')
+        else:
+            self.write(extended_loop and ', undefined):' or ':')
+
+        self.indent()
+        self.enter_frame(loop_frame)
+
+        self.blockvisit(node.body, loop_frame)
+        if node.else_:
+            self.writeline('%s = 0' % iteration_indicator)
+        self.outdent()
+        self.leave_frame(loop_frame, with_python_scope=node.recursive
+                         and not node.else_)
+
+        if node.else_:
+            self.writeline('if %s:' % iteration_indicator)
+            self.indent()
+            self.enter_frame(else_frame)
+            self.blockvisit(node.else_, else_frame)
+            self.leave_frame(else_frame)
+            self.outdent()
+
+        # if the node was recursive we have to return the buffer contents
+        # and start the iteration code
+        if node.recursive:
+            self.return_buffer_contents(loop_frame)
+            self.outdent()
+            self.start_write(frame, node)
+            if self.environment.is_async:
+                self.write('await ')
+            self.write('loop(')
+            if self.environment.is_async:
+                self.write('auto_aiter(')
+            self.visit(node.iter, frame)
+            if self.environment.is_async:
+                self.write(')')
+            self.write(', loop)')
+            self.end_write(frame)
+
+    def visit_If(self, node, frame):
+        if_frame = frame.soft()
+        self.writeline('if ', node)
+        self.visit(node.test, if_frame)
+        self.write(':')
+        self.indent()
+        self.blockvisit(node.body, if_frame)
+        self.outdent()
+        for elif_ in node.elif_:
+            self.writeline('elif ', elif_)
+            self.visit(elif_.test, if_frame)
+            self.write(':')
+            self.indent()
+            self.blockvisit(elif_.body, if_frame)
+            self.outdent()
+        if node.else_:
+            self.writeline('else:')
+            self.indent()
+            self.blockvisit(node.else_, if_frame)
+            self.outdent()
+
+    def visit_Macro(self, node, frame):
+        macro_frame, macro_ref = self.macro_body(node, frame)
+        self.newline()
+        if frame.toplevel:
+            if not node.name.startswith('_'):
+                self.write('context.exported_vars.add(%r)' % node.name)
+            ref = frame.symbols.ref(node.name)
+            self.writeline('context.vars[%r] = ' % node.name)
+        self.write('%s = ' % frame.symbols.ref(node.name))
+        self.macro_def(macro_ref, macro_frame)
+
+    def visit_CallBlock(self, node, frame):
+        call_frame, macro_ref = self.macro_body(node, frame)
+        self.writeline('caller = ')
+        self.macro_def(macro_ref, call_frame)
+        self.start_write(frame, node)
+        self.visit_Call(node.call, frame, forward_caller=True)
+        self.end_write(frame)
+
+    def visit_FilterBlock(self, node, frame):
+        filter_frame = frame.inner()
+        filter_frame.symbols.analyze_node(node)
+        self.enter_frame(filter_frame)
+        self.buffer(filter_frame)
+        self.blockvisit(node.body, filter_frame)
+        self.start_write(frame, node)
+        self.visit_Filter(node.filter, filter_frame)
+        self.end_write(frame)
+        self.leave_frame(filter_frame)
+
+    def visit_With(self, node, frame):
+        with_frame = frame.inner()
+        with_frame.symbols.analyze_node(node)
+        self.enter_frame(with_frame)
+        for idx, (target, expr) in enumerate(izip(node.targets, node.values)):
+            self.newline()
+            self.visit(target, with_frame)
+            self.write(' = ')
+            self.visit(expr, frame)
+        self.blockvisit(node.body, with_frame)
+        self.leave_frame(with_frame)
+
+    def visit_ExprStmt(self, node, frame):
+        self.newline(node)
+        self.visit(node.node, frame)
+
+    _FinalizeInfo = namedtuple("_FinalizeInfo", ("const", "src"))
+    #: The default finalize function if the environment isn't configured
+    #: with one. Or if the environment has one, this is called on that
+    #: function's output for constants.
+    _default_finalize = text_type
+    _finalize = None
+
+    def _make_finalize(self):
+        """Build the finalize function to be used on constants and at
+        runtime. Cached so it's only created once for all output nodes.
+
+        Returns a ``namedtuple`` with the following attributes:
+
+        ``const``
+            A function to finalize constant data at compile time.
+
+        ``src``
+            Source code to output around nodes to be evaluated at
+            runtime.
+        """
+        if self._finalize is not None:
+            return self._finalize
+
+        finalize = default = self._default_finalize
+        src = None
+
+        if self.environment.finalize:
+            src = "environment.finalize("
+            env_finalize = self.environment.finalize
+
+            def finalize(value):
+                return default(env_finalize(value))
+
+            if getattr(env_finalize, "contextfunction", False):
+                src += "context, "
+                finalize = None
+            elif getattr(env_finalize, "evalcontextfunction", False):
+                src += "context.eval_ctx, "
+                finalize = None
+            elif getattr(env_finalize, "environmentfunction", False):
+                src += "environment, "
+
+                def finalize(value):
+                    return default(env_finalize(self.environment, value))
+
+        self._finalize = self._FinalizeInfo(finalize, src)
+        return self._finalize
+
+    def _output_const_repr(self, group):
+        """Given a group of constant values converted from ``Output``
+        child nodes, produce a string to write to the template module
+        source.
+        """
+        return repr(concat(group))
+
+    def _output_child_to_const(self, node, frame, finalize):
+        """Try to optimize a child of an ``Output`` node by trying to
+        convert it to constant, finalized data at compile time.
+
+        If :exc:`Impossible` is raised, the node is not constant and
+        will be evaluated at runtime. Any other exception will also be
+        evaluated at runtime for easier debugging.
+        """
+        const = node.as_const(frame.eval_ctx)
+
+        if frame.eval_ctx.autoescape:
+            const = escape(const)
+
+        # Template data doesn't go through finalize.
+        if isinstance(node, nodes.TemplateData):
+            return text_type(const)
+
+        return finalize.const(const)
+
+    def _output_child_pre(self, node, frame, finalize):
+        """Output extra source code before visiting a child of an
+        ``Output`` node.
+        """
+        if frame.eval_ctx.volatile:
+            self.write("(escape if context.eval_ctx.autoescape else to_string)(")
+        elif frame.eval_ctx.autoescape:
+            self.write("escape(")
+        else:
+            self.write("to_string(")
+
+        if finalize.src is not None:
+            self.write(finalize.src)
+
+    def _output_child_post(self, node, frame, finalize):
+        """Output extra source code after visiting a child of an
+        ``Output`` node.
+        """
+        self.write(")")
+
+        if finalize.src is not None:
+            self.write(")")
+
+    def visit_Output(self, node, frame):
+        # If an extends is active, don't render outside a block.
+        if frame.require_output_check:
+            # A top-level extends is known to exist at compile time.
+            if self.has_known_extends:
+                return
+
+            self.writeline("if parent_template is None:")
+            self.indent()
+
+        finalize = self._make_finalize()
+        body = []
+
+        # Evaluate constants at compile time if possible. Each item in
+        # body will be either a list of static data or a node to be
+        # evaluated at runtime.
+        for child in node.nodes:
+            try:
+                if not (
+                    # If the finalize function requires runtime context,
+                    # constants can't be evaluated at compile time.
+                    finalize.const
+                    # Unless it's basic template data that won't be
+                    # finalized anyway.
+                    or isinstance(child, nodes.TemplateData)
+                ):
+                    raise nodes.Impossible()
+
+                const = self._output_child_to_const(child, frame, finalize)
+            except (nodes.Impossible, Exception):
+                # The node was not constant and needs to be evaluated at
+                # runtime. Or another error was raised, which is easier
+                # to debug at runtime.
+                body.append(child)
+                continue
+
+            if body and isinstance(body[-1], list):
+                body[-1].append(const)
+            else:
+                body.append([const])
+
+        if frame.buffer is not None:
+            if len(body) == 1:
+                self.writeline("%s.append(" % frame.buffer)
+            else:
+                self.writeline("%s.extend((" % frame.buffer)
+
+            self.indent()
+
+        for item in body:
+            if isinstance(item, list):
+                # A group of constant data to join and output.
+                val = self._output_const_repr(item)
+
+                if frame.buffer is None:
+                    self.writeline("yield " + val)
+                else:
+                    self.writeline(val + ",")
+            else:
+                if frame.buffer is None:
+                    self.writeline("yield ", item)
+                else:
+                    self.newline(item)
+
+                # A node to be evaluated at runtime.
+                self._output_child_pre(item, frame, finalize)
+                self.visit(item, frame)
+                self._output_child_post(item, frame, finalize)
+
+                if frame.buffer is not None:
+                    self.write(",")
+
+        if frame.buffer is not None:
+            self.outdent()
+            self.writeline(")" if len(body) == 1 else "))")
+
+        if frame.require_output_check:
+            self.outdent()
+
+    def visit_Assign(self, node, frame):
+        self.push_assign_tracking()
+        self.newline(node)
+        self.visit(node.target, frame)
+        self.write(' = ')
+        self.visit(node.node, frame)
+        self.pop_assign_tracking(frame)
+
+    def visit_AssignBlock(self, node, frame):
+        self.push_assign_tracking()
+        block_frame = frame.inner()
+        # This is a special case.  Since a set block always captures we
+        # will disable output checks.  This way one can use set blocks
+        # toplevel even in extended templates.
+        block_frame.require_output_check = False
+        block_frame.symbols.analyze_node(node)
+        self.enter_frame(block_frame)
+        self.buffer(block_frame)
+        self.blockvisit(node.body, block_frame)
+        self.newline(node)
+        self.visit(node.target, frame)
+        self.write(' = (Markup if context.eval_ctx.autoescape '
+                   'else identity)(')
+        if node.filter is not None:
+            self.visit_Filter(node.filter, block_frame)
+        else:
+            self.write('concat(%s)' % block_frame.buffer)
+        self.write(')')
+        self.pop_assign_tracking(frame)
+        self.leave_frame(block_frame)
+
+    # -- Expression Visitors
+
+    def visit_Name(self, node, frame):
+        if node.ctx == 'store' and frame.toplevel:
+            if self._assign_stack:
+                self._assign_stack[-1].add(node.name)
+        ref = frame.symbols.ref(node.name)
+
+        # If we are looking up a variable we might have to deal with the
+        # case where it's undefined.  We can skip that case if the load
+        # instruction indicates a parameter which are always defined.
+        if node.ctx == 'load':
+            load = frame.symbols.find_load(ref)
+            if not (load is not None and load[0] == VAR_LOAD_PARAMETER and \
+                    not self.parameter_is_undeclared(ref)):
+                self.write('(undefined(name=%r) if %s is missing else %s)' %
+                           (node.name, ref, ref))
+                return
+
+        self.write(ref)
+
+    def visit_NSRef(self, node, frame):
+        # NSRefs can only be used to store values; since they use the normal
+        # `foo.bar` notation they will be parsed as a normal attribute access
+        # when used anywhere but in a `set` context
+        ref = frame.symbols.ref(node.name)
+        self.writeline('if not isinstance(%s, Namespace):' % ref)
+        self.indent()
+        self.writeline('raise TemplateRuntimeError(%r)' %
+                       'cannot assign attribute on non-namespace object')
+        self.outdent()
+        self.writeline('%s[%r]' % (ref, node.attr))
+
+    def visit_Const(self, node, frame):
+        val = node.as_const(frame.eval_ctx)
+        if isinstance(val, float):
+            self.write(str(val))
+        else:
+            self.write(repr(val))
+
+    def visit_TemplateData(self, node, frame):
+        try:
+            self.write(repr(node.as_const(frame.eval_ctx)))
+        except nodes.Impossible:
+            self.write('(Markup if context.eval_ctx.autoescape else identity)(%r)'
+                       % node.data)
+
+    def visit_Tuple(self, node, frame):
+        self.write('(')
+        idx = -1
+        for idx, item in enumerate(node.items):
+            if idx:
+                self.write(', ')
+            self.visit(item, frame)
+        self.write(idx == 0 and ',)' or ')')
+
+    def visit_List(self, node, frame):
+        self.write('[')
+        for idx, item in enumerate(node.items):
+            if idx:
+                self.write(', ')
+            self.visit(item, frame)
+        self.write(']')
+
+    def visit_Dict(self, node, frame):
+        self.write('{')
+        for idx, item in enumerate(node.items):
+            if idx:
+                self.write(', ')
+            self.visit(item.key, frame)
+            self.write(': ')
+            self.visit(item.value, frame)
+        self.write('}')
+
+    def binop(operator, interceptable=True):
+        @optimizeconst
+        def visitor(self, node, frame):
+            if self.environment.sandboxed and \
+               operator in self.environment.intercepted_binops:
+                self.write('environment.call_binop(context, %r, ' % operator)
+                self.visit(node.left, frame)
+                self.write(', ')
+                self.visit(node.right, frame)
+            else:
+                self.write('(')
+                self.visit(node.left, frame)
+                self.write(' %s ' % operator)
+                self.visit(node.right, frame)
+            self.write(')')
+        return visitor
+
+    def uaop(operator, interceptable=True):
+        @optimizeconst
+        def visitor(self, node, frame):
+            if self.environment.sandboxed and \
+               operator in self.environment.intercepted_unops:
+                self.write('environment.call_unop(context, %r, ' % operator)
+                self.visit(node.node, frame)
+            else:
+                self.write('(' + operator)
+                self.visit(node.node, frame)
+            self.write(')')
+        return visitor
+
+    visit_Add = binop('+')
+    visit_Sub = binop('-')
+    visit_Mul = binop('*')
+    visit_Div = binop('/')
+    visit_FloorDiv = binop('//')
+    visit_Pow = binop('**')
+    visit_Mod = binop('%')
+    visit_And = binop('and', interceptable=False)
+    visit_Or = binop('or', interceptable=False)
+    visit_Pos = uaop('+')
+    visit_Neg = uaop('-')
+    visit_Not = uaop('not ', interceptable=False)
+    del binop, uaop
+
+    @optimizeconst
+    def visit_Concat(self, node, frame):
+        if frame.eval_ctx.volatile:
+            func_name = '(context.eval_ctx.volatile and' \
+                        ' markup_join or unicode_join)'
+        elif frame.eval_ctx.autoescape:
+            func_name = 'markup_join'
+        else:
+            func_name = 'unicode_join'
+        self.write('%s((' % func_name)
+        for arg in node.nodes:
+            self.visit(arg, frame)
+            self.write(', ')
+        self.write('))')
+
+    @optimizeconst
+    def visit_Compare(self, node, frame):
+        self.write('(')
+        self.visit(node.expr, frame)
+        for op in node.ops:
+            self.visit(op, frame)
+        self.write(')')
+
+    def visit_Operand(self, node, frame):
+        self.write(' %s ' % operators[node.op])
+        self.visit(node.expr, frame)
+
+    @optimizeconst
+    def visit_Getattr(self, node, frame):
+        if self.environment.is_async:
+            self.write("await auto_await(")
+
+        self.write('environment.getattr(')
+        self.visit(node.node, frame)
+        self.write(', %r)' % node.attr)
+
+        if self.environment.is_async:
+            self.write(")")
+
+    @optimizeconst
+    def visit_Getitem(self, node, frame):
+        # slices bypass the environment getitem method.
+        if isinstance(node.arg, nodes.Slice):
+            self.visit(node.node, frame)
+            self.write('[')
+            self.visit(node.arg, frame)
+            self.write(']')
+        else:
+            if self.environment.is_async:
+                self.write("await auto_await(")
+
+            self.write('environment.getitem(')
+            self.visit(node.node, frame)
+            self.write(', ')
+            self.visit(node.arg, frame)
+            self.write(')')
+
+            if self.environment.is_async:
+                self.write(")")
+
+    def visit_Slice(self, node, frame):
+        if node.start is not None:
+            self.visit(node.start, frame)
+        self.write(':')
+        if node.stop is not None:
+            self.visit(node.stop, frame)
+        if node.step is not None:
+            self.write(':')
+            self.visit(node.step, frame)
+
+    @optimizeconst
+    def visit_Filter(self, node, frame):
+        if self.environment.is_async:
+            self.write('await auto_await(')
+        self.write(self.filters[node.name] + '(')
+        func = self.environment.filters.get(node.name)
+        if func is None:
+            self.fail('no filter named %r' % node.name, node.lineno)
+        if getattr(func, 'contextfilter', False):
+            self.write('context, ')
+        elif getattr(func, 'evalcontextfilter', False):
+            self.write('context.eval_ctx, ')
+        elif getattr(func, 'environmentfilter', False):
+            self.write('environment, ')
+
+        # if the filter node is None we are inside a filter block
+        # and want to write to the current buffer
+        if node.node is not None:
+            self.visit(node.node, frame)
+        elif frame.eval_ctx.volatile:
+            self.write('(context.eval_ctx.autoescape and'
+                       ' Markup(concat(%s)) or concat(%s))' %
+                       (frame.buffer, frame.buffer))
+        elif frame.eval_ctx.autoescape:
+            self.write('Markup(concat(%s))' % frame.buffer)
+        else:
+            self.write('concat(%s)' % frame.buffer)
+        self.signature(node, frame)
+        self.write(')')
+        if self.environment.is_async:
+            self.write(')')
+
+    @optimizeconst
+    def visit_Test(self, node, frame):
+        self.write(self.tests[node.name] + '(')
+        if node.name not in self.environment.tests:
+            self.fail('no test named %r' % node.name, node.lineno)
+        self.visit(node.node, frame)
+        self.signature(node, frame)
+        self.write(')')
+
+    @optimizeconst
+    def visit_CondExpr(self, node, frame):
+        def write_expr2():
+            if node.expr2 is not None:
+                return self.visit(node.expr2, frame)
+            self.write('cond_expr_undefined(%r)' % ('the inline if-'
+                       'expression on %s evaluated to false and '
+                       'no else section was defined.' % self.position(node)))
+
+        self.write('(')
+        self.visit(node.expr1, frame)
+        self.write(' if ')
+        self.visit(node.test, frame)
+        self.write(' else ')
+        write_expr2()
+        self.write(')')
+
+    @optimizeconst
+    def visit_Call(self, node, frame, forward_caller=False):
+        if self.environment.is_async:
+            self.write('await auto_await(')
+        if self.environment.sandboxed:
+            self.write('environment.call(context, ')
+        else:
+            self.write('context.call(')
+        self.visit(node.node, frame)
+        extra_kwargs = forward_caller and {'caller': 'caller'} or None
+        self.signature(node, frame, extra_kwargs)
+        self.write(')')
+        if self.environment.is_async:
+            self.write(')')
+
+    def visit_Keyword(self, node, frame):
+        self.write(node.key + '=')
+        self.visit(node.value, frame)
+
+    # -- Unused nodes for extensions
+
+    def visit_MarkSafe(self, node, frame):
+        self.write('Markup(')
+        self.visit(node.expr, frame)
+        self.write(')')
+
+    def visit_MarkSafeIfAutoescape(self, node, frame):
+        self.write('(context.eval_ctx.autoescape and Markup or identity)(')
+        self.visit(node.expr, frame)
+        self.write(')')
+
+    def visit_EnvironmentAttribute(self, node, frame):
+        self.write('environment.' + node.name)
+
+    def visit_ExtensionAttribute(self, node, frame):
+        self.write('environment.extensions[%r].%s' % (node.identifier, node.name))
+
+    def visit_ImportedName(self, node, frame):
+        self.write(self.import_aliases[node.importname])
+
+    def visit_InternalName(self, node, frame):
+        self.write(node.name)
+
+    def visit_ContextReference(self, node, frame):
+        self.write('context')
+
+    def visit_DerivedContextReference(self, node, frame):
+        self.write(self.derive_context(frame))
+
+    def visit_Continue(self, node, frame):
+        self.writeline('continue', node)
+
+    def visit_Break(self, node, frame):
+        self.writeline('break', node)
+
+    def visit_Scope(self, node, frame):
+        scope_frame = frame.inner()
+        scope_frame.symbols.analyze_node(node)
+        self.enter_frame(scope_frame)
+        self.blockvisit(node.body, scope_frame)
+        self.leave_frame(scope_frame)
+
+    def visit_OverlayScope(self, node, frame):
+        ctx = self.temporary_identifier()
+        self.writeline('%s = %s' % (ctx, self.derive_context(frame)))
+        self.writeline('%s.vars = ' % ctx)
+        self.visit(node.context, frame)
+        self.push_context_reference(ctx)
+
+        scope_frame = frame.inner(isolated=True)
+        scope_frame.symbols.analyze_node(node)
+        self.enter_frame(scope_frame)
+        self.blockvisit(node.body, scope_frame)
+        self.leave_frame(scope_frame)
+        self.pop_context_reference()
+
+    def visit_EvalContextModifier(self, node, frame):
+        for keyword in node.options:
+            self.writeline('context.eval_ctx.%s = ' % keyword.key)
+            self.visit(keyword.value, frame)
+            try:
+                val = keyword.value.as_const(frame.eval_ctx)
+            except nodes.Impossible:
+                frame.eval_ctx.volatile = True
+            else:
+                setattr(frame.eval_ctx, keyword.key, val)
+
+    def visit_ScopedEvalContextModifier(self, node, frame):
+        old_ctx_name = self.temporary_identifier()
+        saved_ctx = frame.eval_ctx.save()
+        self.writeline('%s = context.eval_ctx.save()' % old_ctx_name)
+        self.visit_EvalContextModifier(node, frame)
+        for child in node.body:
+            self.visit(child, frame)
+        frame.eval_ctx.revert(saved_ctx)
+        self.writeline('context.eval_ctx.revert(%s)' % old_ctx_name)
diff --git a/src/jinja2/constants.py b/src/jinja2/constants.py
new file mode 100644
index 0000000..11efd1e
--- /dev/null
+++ b/src/jinja2/constants.py
@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja.constants
+    ~~~~~~~~~~~~~~~
+
+    Various constants.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+
+
+#: list of lorem ipsum words used by the lipsum() helper function
+LOREM_IPSUM_WORDS = u'''\
+a ac accumsan ad adipiscing aenean aliquam aliquet amet ante aptent arcu at
+auctor augue bibendum blandit class commodo condimentum congue consectetuer
+consequat conubia convallis cras cubilia cum curabitur curae cursus dapibus
+diam dictum dictumst dignissim dis dolor donec dui duis egestas eget eleifend
+elementum elit enim erat eros est et etiam eu euismod facilisi facilisis fames
+faucibus felis fermentum feugiat fringilla fusce gravida habitant habitasse hac
+hendrerit hymenaeos iaculis id imperdiet in inceptos integer interdum ipsum
+justo lacinia lacus laoreet lectus leo libero ligula litora lobortis lorem
+luctus maecenas magna magnis malesuada massa mattis mauris metus mi molestie
+mollis montes morbi mus nam nascetur natoque nec neque netus nibh nisi nisl non
+nonummy nostra nulla nullam nunc odio orci ornare parturient pede pellentesque
+penatibus per pharetra phasellus placerat platea porta porttitor posuere
+potenti praesent pretium primis proin pulvinar purus quam quis quisque rhoncus
+ridiculus risus rutrum sagittis sapien scelerisque sed sem semper senectus sit
+sociis sociosqu sodales sollicitudin suscipit suspendisse taciti tellus tempor
+tempus tincidunt torquent tortor tristique turpis ullamcorper ultrices
+ultricies urna ut varius vehicula vel velit venenatis vestibulum vitae vivamus
+viverra volutpat vulputate'''
diff --git a/src/jinja2/debug.py b/src/jinja2/debug.py
new file mode 100644
index 0000000..4370b79
--- /dev/null
+++ b/src/jinja2/debug.py
@@ -0,0 +1,266 @@
+import sys
+from types import CodeType
+
+from jinja2 import TemplateSyntaxError
+from jinja2._compat import PYPY
+from jinja2.utils import internal_code
+from jinja2.utils import missing
+
+
+def rewrite_traceback_stack(source=None):
+    """Rewrite the current exception to replace any tracebacks from
+    within compiled template code with tracebacks that look like they
+    came from the template source.
+
+    This must be called within an ``except`` block.
+
+    :param exc_info: A :meth:`sys.exc_info` tuple. If not provided,
+        the current ``exc_info`` is used.
+    :param source: For ``TemplateSyntaxError``, the original source if
+        known.
+    :return: A :meth:`sys.exc_info` tuple that can be re-raised.
+    """
+    exc_type, exc_value, tb = sys.exc_info()
+
+    if isinstance(exc_value, TemplateSyntaxError) and not exc_value.translated:
+        exc_value.translated = True
+        exc_value.source = source
+
+        try:
+            # Remove the old traceback on Python 3, otherwise the frames
+            # from the compiler still show up.
+            exc_value.with_traceback(None)
+        except AttributeError:
+            pass
+
+        # Outside of runtime, so the frame isn't executing template
+        # code, but it still needs to point at the template.
+        tb = fake_traceback(
+            exc_value, None, exc_value.filename or "<unknown>", exc_value.lineno
+        )
+    else:
+        # Skip the frame for the render function.
+        tb = tb.tb_next
+
+    stack = []
+
+    # Build the stack of traceback object, replacing any in template
+    # code with the source file and line information.
+    while tb is not None:
+        # Skip frames decorated with @internalcode. These are internal
+        # calls that aren't useful in template debugging output.
+        if tb.tb_frame.f_code in internal_code:
+            tb = tb.tb_next
+            continue
+
+        template = tb.tb_frame.f_globals.get("__jinja_template__")
+
+        if template is not None:
+            lineno = template.get_corresponding_lineno(tb.tb_lineno)
+            fake_tb = fake_traceback(exc_value, tb, template.filename, lineno)
+            stack.append(fake_tb)
+        else:
+            stack.append(tb)
+
+        tb = tb.tb_next
+
+    tb_next = None
+
+    # Assign tb_next in reverse to avoid circular references.
+    for tb in reversed(stack):
+        tb_next = tb_set_next(tb, tb_next)
+
+    return exc_type, exc_value, tb_next
+
+
+def fake_traceback(exc_value, tb, filename, lineno):
+    """Produce a new traceback object that looks like it came from the
+    template source instead of the compiled code. The filename, line
+    number, and location name will point to the template, and the local
+    variables will be the current template context.
+
+    :param exc_value: The original exception to be re-raised to create
+        the new traceback.
+    :param tb: The original traceback to get the local variables and
+        code info from.
+    :param filename: The template filename.
+    :param lineno: The line number in the template source.
+    """
+    if tb is not None:
+        # Replace the real locals with the context that would be
+        # available at that point in the template.
+        locals = get_template_locals(tb.tb_frame.f_locals)
+        locals.pop("__jinja_exception__", None)
+    else:
+        locals = {}
+
+    globals = {
+        "__name__": filename,
+        "__file__": filename,
+        "__jinja_exception__": exc_value,
+    }
+    # Raise an exception at the correct line number.
+    code = compile('\n' * (lineno - 1) + "raise __jinja_exception__", filename, "exec")
+
+    # Build a new code object that points to the template file and
+    # replaces the location with a block name.
+    try:
+        location = "template"
+
+        if tb is not None:
+            function = tb.tb_frame.f_code.co_name
+
+            if function == "root":
+                location = "top-level template code"
+            elif function.startswith("block_"):
+                location = 'block "%s"' % function[6:]
+
+        # Collect arguments for the new code object. CodeType only
+        # accepts positional arguments, and arguments were inserted in
+        # new Python versions.
+        code_args = []
+
+        for attr in (
+            "argcount",
+            "posonlyargcount",  # Python 3.8
+            "kwonlyargcount",  # Python 3
+            "nlocals",
+            "stacksize",
+            "flags",
+            "code",  # codestring
+            "consts",  # constants
+            "names",
+            "varnames",
+            ("filename", filename),
+            ("name", location),
+            "firstlineno",
+            "lnotab",
+            "freevars",
+            "cellvars",
+        ):
+            if isinstance(attr, tuple):
+                # Replace with given value.
+                code_args.append(attr[1])
+                continue
+
+            try:
+                # Copy original value if it exists.
+                code_args.append(getattr(code, "co_" + attr))
+            except AttributeError:
+                # Some arguments were added later.
+                continue
+
+        code = CodeType(*code_args)
+    except Exception:
+        # Some environments such as Google App Engine don't support
+        # modifying code objects.
+        pass
+
+    # Execute the new code, which is guaranteed to raise, and return
+    # the new traceback without this frame.
+    try:
+        exec(code, globals, locals)
+    except:
+        return sys.exc_info()[2].tb_next
+
+
+def get_template_locals(real_locals):
+    """Based on the runtime locals, get the context that would be
+    available at that point in the template.
+    """
+    # Start with the current template context.
+    ctx = real_locals.get("context")
+
+    if ctx:
+        data = ctx.get_all().copy()
+    else:
+        data = {}
+
+    # Might be in a derived context that only sets local variables
+    # rather than pushing a context. Local variables follow the scheme
+    # l_depth_name. Find the highest-depth local that has a value for
+    # each name.
+    local_overrides = {}
+
+    for name, value in real_locals.items():
+        if not name.startswith("l_") or value is missing:
+            # Not a template variable, or no longer relevant.
+            continue
+
+        try:
+            _, depth, name = name.split("_", 2)
+            depth = int(depth)
+        except ValueError:
+            continue
+
+        cur_depth = local_overrides.get(name, (-1,))[0]
+
+        if cur_depth < depth:
+            local_overrides[name] = (depth, value)
+
+    # Modify the context with any derived context.
+    for name, (_, value) in local_overrides.items():
+        if value is missing:
+            data.pop(name, None)
+        else:
+            data[name] = value
+
+    return data
+
+
+if sys.version_info >= (3, 7):
+    # tb_next is directly assignable as of Python 3.7
+    def tb_set_next(tb, tb_next):
+        tb.tb_next = tb_next
+        return tb
+elif PYPY:
+    # PyPy might have special support, and won't work with ctypes.
+    try:
+        import tputil
+    except ImportError:
+        # Without tproxy support, use the original traceback.
+        def tb_set_next(tb, tb_next):
+            return tb
+    else:
+        # With tproxy support, create a proxy around the traceback that
+        # returns the new tb_next.
+        def tb_set_next(tb, tb_next):
+            def controller(op):
+                if op.opname == "__getattribute__" and op.args[0] == "tb_next":
+                    return tb_next
+
+                return op.delegate()
+
+            return tputil.make_proxy(controller, obj=tb)
+else:
+    # Use ctypes to assign tb_next at the C level since it's read-only
+    # from Python.
+    import ctypes
+
+    class _CTraceback(ctypes.Structure):
+        _fields_ = [
+            # Extra PyObject slots when compiled with Py_TRACE_REFS.
+            (
+                "PyObject_HEAD",
+                ctypes.c_byte * (32 if hasattr(sys, "getobjects") else 16),
+            ),
+            # Only care about tb_next as an object, not a traceback.
+            ("tb_next", ctypes.py_object),
+        ]
+
+    def tb_set_next(tb, tb_next):
+        c_tb = _CTraceback.from_address(id(tb))
+
+        # Clear out the old tb_next.
+        if tb.tb_next is not None:
+            c_tb_next = ctypes.py_object(tb.tb_next)
+            c_tb.tb_next = ctypes.py_object()
+            ctypes.pythonapi.Py_DecRef(c_tb_next)
+
+        # Assign the new tb_next.
+        if tb_next is not None:
+            c_tb_next = ctypes.py_object(tb_next)
+            ctypes.pythonapi.Py_IncRef(c_tb_next)
+            c_tb.tb_next = c_tb_next
+
+        return tb
diff --git a/src/jinja2/defaults.py b/src/jinja2/defaults.py
new file mode 100644
index 0000000..7c93dec
--- /dev/null
+++ b/src/jinja2/defaults.py
@@ -0,0 +1,56 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.defaults
+    ~~~~~~~~~~~~~~~
+
+    Jinja default filters and tags.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+from jinja2._compat import range_type
+from jinja2.utils import generate_lorem_ipsum, Cycler, Joiner, Namespace
+
+
+# defaults for the parser / lexer
+BLOCK_START_STRING = '{%'
+BLOCK_END_STRING = '%}'
+VARIABLE_START_STRING = '{{'
+VARIABLE_END_STRING = '}}'
+COMMENT_START_STRING = '{#'
+COMMENT_END_STRING = '#}'
+LINE_STATEMENT_PREFIX = None
+LINE_COMMENT_PREFIX = None
+TRIM_BLOCKS = False
+LSTRIP_BLOCKS = False
+NEWLINE_SEQUENCE = '\n'
+KEEP_TRAILING_NEWLINE = False
+
+
+# default filters, tests and namespace
+from jinja2.filters import FILTERS as DEFAULT_FILTERS
+from jinja2.tests import TESTS as DEFAULT_TESTS
+DEFAULT_NAMESPACE = {
+    'range':        range_type,
+    'dict':         dict,
+    'lipsum':       generate_lorem_ipsum,
+    'cycler':       Cycler,
+    'joiner':       Joiner,
+    'namespace':    Namespace
+}
+
+
+# default policies
+DEFAULT_POLICIES = {
+    'compiler.ascii_str':   True,
+    'urlize.rel':           'noopener',
+    'urlize.target':        None,
+    'truncate.leeway':      5,
+    'json.dumps_function':  None,
+    'json.dumps_kwargs':    {'sort_keys': True},
+    'ext.i18n.trimmed':     False,
+}
+
+
+# export all constants
+__all__ = tuple(x for x in locals().keys() if x.isupper())
diff --git a/src/jinja2/environment.py b/src/jinja2/environment.py
new file mode 100644
index 0000000..1209e9d
--- /dev/null
+++ b/src/jinja2/environment.py
@@ -0,0 +1,1264 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.environment
+    ~~~~~~~~~~~~~~~~~~
+
+    Provides a class that holds runtime and parsing time options.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import os
+import sys
+import weakref
+from functools import reduce, partial
+from jinja2 import nodes
+from jinja2.defaults import BLOCK_START_STRING, \
+     BLOCK_END_STRING, VARIABLE_START_STRING, VARIABLE_END_STRING, \
+     COMMENT_START_STRING, COMMENT_END_STRING, LINE_STATEMENT_PREFIX, \
+     LINE_COMMENT_PREFIX, TRIM_BLOCKS, NEWLINE_SEQUENCE, \
+     DEFAULT_FILTERS, DEFAULT_TESTS, DEFAULT_NAMESPACE, \
+     DEFAULT_POLICIES, KEEP_TRAILING_NEWLINE, LSTRIP_BLOCKS
+from jinja2.lexer import get_lexer, TokenStream
+from jinja2.parser import Parser
+from jinja2.nodes import EvalContext
+from jinja2.compiler import generate, CodeGenerator
+from jinja2.runtime import Undefined, new_context, Context
+from jinja2.exceptions import TemplateSyntaxError, TemplateNotFound, \
+     TemplatesNotFound, TemplateRuntimeError, UndefinedError
+from jinja2.utils import import_string, LRUCache, Markup, missing, \
+     concat, consume, internalcode, have_async_gen
+from jinja2._compat import imap, ifilter, string_types, iteritems, \
+     text_type, reraise, implements_iterator, implements_to_string, \
+     encode_filename, PY2, PYPY
+
+
+# for direct template usage we have up to ten living environments
+_spontaneous_environments = LRUCache(10)
+
+
+def get_spontaneous_environment(cls, *args):
+    """Return a new spontaneous environment. A spontaneous environment
+    is used for templates created directly rather than through an
+    existing environment.
+
+    :param cls: Environment class to create.
+    :param args: Positional arguments passed to environment.
+    """
+    key = (cls, args)
+
+    try:
+        return _spontaneous_environments[key]
+    except KeyError:
+        _spontaneous_environments[key] = env = cls(*args)
+        env.shared = True
+        return env
+
+
+def create_cache(size):
+    """Return the cache class for the given size."""
+    if size == 0:
+        return None
+    if size < 0:
+        return {}
+    return LRUCache(size)
+
+
+def copy_cache(cache):
+    """Create an empty copy of the given cache."""
+    if cache is None:
+        return None
+    elif type(cache) is dict:
+        return {}
+    return LRUCache(cache.capacity)
+
+
+def load_extensions(environment, extensions):
+    """Load the extensions from the list and bind it to the environment.
+    Returns a dict of instantiated environments.
+    """
+    result = {}
+    for extension in extensions:
+        if isinstance(extension, string_types):
+            extension = import_string(extension)
+        result[extension.identifier] = extension(environment)
+    return result
+
+
+def fail_for_missing_callable(string, name):
+    msg = string % name
+    if isinstance(name, Undefined):
+        try:
+            name._fail_with_undefined_error()
+        except Exception as e:
+            msg = '%s (%s; did you forget to quote the callable name?)' % (msg, e)
+    raise TemplateRuntimeError(msg)
+
+
+def _environment_sanity_check(environment):
+    """Perform a sanity check on the environment."""
+    assert issubclass(environment.undefined, Undefined), 'undefined must ' \
+        'be a subclass of undefined because filters depend on it.'
+    assert environment.block_start_string != \
+        environment.variable_start_string != \
+        environment.comment_start_string, 'block, variable and comment ' \
+        'start strings must be different'
+    assert environment.newline_sequence in ('\r', '\r\n', '\n'), \
+        'newline_sequence set to unknown line ending string.'
+    return environment
+
+
+class Environment(object):
+    r"""The core component of Jinja is the `Environment`.  It contains
+    important shared variables like configuration, filters, tests,
+    globals and others.  Instances of this class may be modified if
+    they are not shared and if no template was loaded so far.
+    Modifications on environments after the first template was loaded
+    will lead to surprising effects and undefined behavior.
+
+    Here are the possible initialization parameters:
+
+        `block_start_string`
+            The string marking the beginning of a block.  Defaults to ``'{%'``.
+
+        `block_end_string`
+            The string marking the end of a block.  Defaults to ``'%}'``.
+
+        `variable_start_string`
+            The string marking the beginning of a print statement.
+            Defaults to ``'{{'``.
+
+        `variable_end_string`
+            The string marking the end of a print statement.  Defaults to
+            ``'}}'``.
+
+        `comment_start_string`
+            The string marking the beginning of a comment.  Defaults to ``'{#'``.
+
+        `comment_end_string`
+            The string marking the end of a comment.  Defaults to ``'#}'``.
+
+        `line_statement_prefix`
+            If given and a string, this will be used as prefix for line based
+            statements.  See also :ref:`line-statements`.
+
+        `line_comment_prefix`
+            If given and a string, this will be used as prefix for line based
+            comments.  See also :ref:`line-statements`.
+
+            .. versionadded:: 2.2
+
+        `trim_blocks`
+            If this is set to ``True`` the first newline after a block is
+            removed (block, not variable tag!).  Defaults to `False`.
+
+        `lstrip_blocks`
+            If this is set to ``True`` leading spaces and tabs are stripped
+            from the start of a line to a block.  Defaults to `False`.
+
+        `newline_sequence`
+            The sequence that starts a newline.  Must be one of ``'\r'``,
+            ``'\n'`` or ``'\r\n'``.  The default is ``'\n'`` which is a
+            useful default for Linux and OS X systems as well as web
+            applications.
+
+        `keep_trailing_newline`
+            Preserve the trailing newline when rendering templates.
+            The default is ``False``, which causes a single newline,
+            if present, to be stripped from the end of the template.
+
+            .. versionadded:: 2.7
+
+        `extensions`
+            List of Jinja extensions to use.  This can either be import paths
+            as strings or extension classes.  For more information have a
+            look at :ref:`the extensions documentation <jinja-extensions>`.
+
+        `optimized`
+            should the optimizer be enabled?  Default is ``True``.
+
+        `undefined`
+            :class:`Undefined` or a subclass of it that is used to represent
+            undefined values in the template.
+
+        `finalize`
+            A callable that can be used to process the result of a variable
+            expression before it is output.  For example one can convert
+            ``None`` implicitly into an empty string here.
+
+        `autoescape`
+            If set to ``True`` the XML/HTML autoescaping feature is enabled by
+            default.  For more details about autoescaping see
+            :class:`~jinja2.utils.Markup`.  As of Jinja 2.4 this can also
+            be a callable that is passed the template name and has to
+            return ``True`` or ``False`` depending on autoescape should be
+            enabled by default.
+
+            .. versionchanged:: 2.4
+               `autoescape` can now be a function
+
+        `loader`
+            The template loader for this environment.
+
+        `cache_size`
+            The size of the cache.  Per default this is ``400`` which means
+            that if more than 400 templates are loaded the loader will clean
+            out the least recently used template.  If the cache size is set to
+            ``0`` templates are recompiled all the time, if the cache size is
+            ``-1`` the cache will not be cleaned.
+
+            .. versionchanged:: 2.8
+               The cache size was increased to 400 from a low 50.
+
+        `auto_reload`
+            Some loaders load templates from locations where the template
+            sources may change (ie: file system or database).  If
+            ``auto_reload`` is set to ``True`` (default) every time a template is
+            requested the loader checks if the source changed and if yes, it
+            will reload the template.  For higher performance it's possible to
+            disable that.
+
+        `bytecode_cache`
+            If set to a bytecode cache object, this object will provide a
+            cache for the internal Jinja bytecode so that templates don't
+            have to be parsed if they were not changed.
+
+            See :ref:`bytecode-cache` for more information.
+
+        `enable_async`
+            If set to true this enables async template execution which allows
+            you to take advantage of newer Python features.  This requires
+            Python 3.6 or later.
+    """
+
+    #: if this environment is sandboxed.  Modifying this variable won't make
+    #: the environment sandboxed though.  For a real sandboxed environment
+    #: have a look at jinja2.sandbox.  This flag alone controls the code
+    #: generation by the compiler.
+    sandboxed = False
+
+    #: True if the environment is just an overlay
+    overlayed = False
+
+    #: the environment this environment is linked to if it is an overlay
+    linked_to = None
+
+    #: shared environments have this set to `True`.  A shared environment
+    #: must not be modified
+    shared = False
+
+    #: the class that is used for code generation.  See
+    #: :class:`~jinja2.compiler.CodeGenerator` for more information.
+    code_generator_class = CodeGenerator
+
+    #: the context class thatis used for templates.  See
+    #: :class:`~jinja2.runtime.Context` for more information.
+    context_class = Context
+
+    def __init__(self,
+                 block_start_string=BLOCK_START_STRING,
+                 block_end_string=BLOCK_END_STRING,
+                 variable_start_string=VARIABLE_START_STRING,
+                 variable_end_string=VARIABLE_END_STRING,
+                 comment_start_string=COMMENT_START_STRING,
+                 comment_end_string=COMMENT_END_STRING,
+                 line_statement_prefix=LINE_STATEMENT_PREFIX,
+                 line_comment_prefix=LINE_COMMENT_PREFIX,
+                 trim_blocks=TRIM_BLOCKS,
+                 lstrip_blocks=LSTRIP_BLOCKS,
+                 newline_sequence=NEWLINE_SEQUENCE,
+                 keep_trailing_newline=KEEP_TRAILING_NEWLINE,
+                 extensions=(),
+                 optimized=True,
+                 undefined=Undefined,
+                 finalize=None,
+                 autoescape=False,
+                 loader=None,
+                 cache_size=400,
+                 auto_reload=True,
+                 bytecode_cache=None,
+                 enable_async=False):
+        # !!Important notice!!
+        #   The constructor accepts quite a few arguments that should be
+        #   passed by keyword rather than position.  However it's important to
+        #   not change the order of arguments because it's used at least
+        #   internally in those cases:
+        #       -   spontaneous environments (i18n extension and Template)
+        #       -   unittests
+        #   If parameter changes are required only add parameters at the end
+        #   and don't change the arguments (or the defaults!) of the arguments
+        #   existing already.
+
+        # lexer / parser information
+        self.block_start_string = block_start_string
+        self.block_end_string = block_end_string
+        self.variable_start_string = variable_start_string
+        self.variable_end_string = variable_end_string
+        self.comment_start_string = comment_start_string
+        self.comment_end_string = comment_end_string
+        self.line_statement_prefix = line_statement_prefix
+        self.line_comment_prefix = line_comment_prefix
+        self.trim_blocks = trim_blocks
+        self.lstrip_blocks = lstrip_blocks
+        self.newline_sequence = newline_sequence
+        self.keep_trailing_newline = keep_trailing_newline
+
+        # runtime information
+        self.undefined = undefined
+        self.optimized = optimized
+        self.finalize = finalize
+        self.autoescape = autoescape
+
+        # defaults
+        self.filters = DEFAULT_FILTERS.copy()
+        self.tests = DEFAULT_TESTS.copy()
+        self.globals = DEFAULT_NAMESPACE.copy()
+
+        # set the loader provided
+        self.loader = loader
+        self.cache = create_cache(cache_size)
+        self.bytecode_cache = bytecode_cache
+        self.auto_reload = auto_reload
+
+        # configurable policies
+        self.policies = DEFAULT_POLICIES.copy()
+
+        # load extensions
+        self.extensions = load_extensions(self, extensions)
+
+        self.enable_async = enable_async
+        self.is_async = self.enable_async and have_async_gen
+        if self.is_async:
+            import jinja2.asyncsupport  # runs patch_all() once
+
+        _environment_sanity_check(self)
+
+    def add_extension(self, extension):
+        """Adds an extension after the environment was created.
+
+        .. versionadded:: 2.5
+        """
+        self.extensions.update(load_extensions(self, [extension]))
+
+    def extend(self, **attributes):
+        """Add the items to the instance of the environment if they do not exist
+        yet.  This is used by :ref:`extensions <writing-extensions>` to register
+        callbacks and configuration values without breaking inheritance.
+        """
+        for key, value in iteritems(attributes):
+            if not hasattr(self, key):
+                setattr(self, key, value)
+
+    def overlay(self, block_start_string=missing, block_end_string=missing,
+                variable_start_string=missing, variable_end_string=missing,
+                comment_start_string=missing, comment_end_string=missing,
+                line_statement_prefix=missing, line_comment_prefix=missing,
+                trim_blocks=missing, lstrip_blocks=missing,
+                extensions=missing, optimized=missing,
+                undefined=missing, finalize=missing, autoescape=missing,
+                loader=missing, cache_size=missing, auto_reload=missing,
+                bytecode_cache=missing):
+        """Create a new overlay environment that shares all the data with the
+        current environment except for cache and the overridden attributes.
+        Extensions cannot be removed for an overlayed environment.  An overlayed
+        environment automatically gets all the extensions of the environment it
+        is linked to plus optional extra extensions.
+
+        Creating overlays should happen after the initial environment was set
+        up completely.  Not all attributes are truly linked, some are just
+        copied over so modifications on the original environment may not shine
+        through.
+        """
+        args = dict(locals())
+        del args['self'], args['cache_size'], args['extensions']
+
+        rv = object.__new__(self.__class__)
+        rv.__dict__.update(self.__dict__)
+        rv.overlayed = True
+        rv.linked_to = self
+
+        for key, value in iteritems(args):
+            if value is not missing:
+                setattr(rv, key, value)
+
+        if cache_size is not missing:
+            rv.cache = create_cache(cache_size)
+        else:
+            rv.cache = copy_cache(self.cache)
+
+        rv.extensions = {}
+        for key, value in iteritems(self.extensions):
+            rv.extensions[key] = value.bind(rv)
+        if extensions is not missing:
+            rv.extensions.update(load_extensions(rv, extensions))
+
+        return _environment_sanity_check(rv)
+
+    lexer = property(get_lexer, doc="The lexer for this environment.")
+
+    def iter_extensions(self):
+        """Iterates over the extensions by priority."""
+        return iter(sorted(self.extensions.values(),
+                           key=lambda x: x.priority))
+
+    def getitem(self, obj, argument):
+        """Get an item or attribute of an object but prefer the item."""
+        try:
+            return obj[argument]
+        except (AttributeError, TypeError, LookupError):
+            if isinstance(argument, string_types):
+                try:
+                    attr = str(argument)
+                except Exception:
+                    pass
+                else:
+                    try:
+                        return getattr(obj, attr)
+                    except AttributeError:
+                        pass
+            return self.undefined(obj=obj, name=argument)
+
+    def getattr(self, obj, attribute):
+        """Get an item or attribute of an object but prefer the attribute.
+        Unlike :meth:`getitem` the attribute *must* be a bytestring.
+        """
+        try:
+            return getattr(obj, attribute)
+        except AttributeError:
+            pass
+        try:
+            return obj[attribute]
+        except (TypeError, LookupError, AttributeError):
+            return self.undefined(obj=obj, name=attribute)
+
+    def call_filter(self, name, value, args=None, kwargs=None,
+                    context=None, eval_ctx=None):
+        """Invokes a filter on a value the same way the compiler does it.
+
+        Note that on Python 3 this might return a coroutine in case the
+        filter is running from an environment in async mode and the filter
+        supports async execution.  It's your responsibility to await this
+        if needed.
+
+        .. versionadded:: 2.7
+        """
+        func = self.filters.get(name)
+        if func is None:
+            fail_for_missing_callable('no filter named %r', name)
+        args = [value] + list(args or ())
+        if getattr(func, 'contextfilter', False):
+            if context is None:
+                raise TemplateRuntimeError('Attempted to invoke context '
+                                           'filter without context')
+            args.insert(0, context)
+        elif getattr(func, 'evalcontextfilter', False):
+            if eval_ctx is None:
+                if context is not None:
+                    eval_ctx = context.eval_ctx
+                else:
+                    eval_ctx = EvalContext(self)
+            args.insert(0, eval_ctx)
+        elif getattr(func, 'environmentfilter', False):
+            args.insert(0, self)
+        return func(*args, **(kwargs or {}))
+
+    def call_test(self, name, value, args=None, kwargs=None):
+        """Invokes a test on a value the same way the compiler does it.
+
+        .. versionadded:: 2.7
+        """
+        func = self.tests.get(name)
+        if func is None:
+            fail_for_missing_callable('no test named %r', name)
+        return func(value, *(args or ()), **(kwargs or {}))
+
+    @internalcode
+    def parse(self, source, name=None, filename=None):
+        """Parse the sourcecode and return the abstract syntax tree.  This
+        tree of nodes is used by the compiler to convert the template into
+        executable source- or bytecode.  This is useful for debugging or to
+        extract information from templates.
+
+        If you are :ref:`developing Jinja extensions <writing-extensions>`
+        this gives you a good overview of the node tree generated.
+        """
+        try:
+            return self._parse(source, name, filename)
+        except TemplateSyntaxError:
+            self.handle_exception(source=source)
+
+    def _parse(self, source, name, filename):
+        """Internal parsing function used by `parse` and `compile`."""
+        return Parser(self, source, name, encode_filename(filename)).parse()
+
+    def lex(self, source, name=None, filename=None):
+        """Lex the given sourcecode and return a generator that yields
+        tokens as tuples in the form ``(lineno, token_type, value)``.
+        This can be useful for :ref:`extension development <writing-extensions>`
+        and debugging templates.
+
+        This does not perform preprocessing.  If you want the preprocessing
+        of the extensions to be applied you have to filter source through
+        the :meth:`preprocess` method.
+        """
+        source = text_type(source)
+        try:
+            return self.lexer.tokeniter(source, name, filename)
+        except TemplateSyntaxError:
+            self.handle_exception(source=source)
+
+    def preprocess(self, source, name=None, filename=None):
+        """Preprocesses the source with all extensions.  This is automatically
+        called for all parsing and compiling methods but *not* for :meth:`lex`
+        because there you usually only want the actual source tokenized.
+        """
+        return reduce(lambda s, e: e.preprocess(s, name, filename),
+                      self.iter_extensions(), text_type(source))
+
+    def _tokenize(self, source, name, filename=None, state=None):
+        """Called by the parser to do the preprocessing and filtering
+        for all the extensions.  Returns a :class:`~jinja2.lexer.TokenStream`.
+        """
+        source = self.preprocess(source, name, filename)
+        stream = self.lexer.tokenize(source, name, filename, state)
+        for ext in self.iter_extensions():
+            stream = ext.filter_stream(stream)
+            if not isinstance(stream, TokenStream):
+                stream = TokenStream(stream, name, filename)
+        return stream
+
+    def _generate(self, source, name, filename, defer_init=False):
+        """Internal hook that can be overridden to hook a different generate
+        method in.
+
+        .. versionadded:: 2.5
+        """
+        return generate(source, self, name, filename, defer_init=defer_init,
+                        optimized=self.optimized)
+
+    def _compile(self, source, filename):
+        """Internal hook that can be overridden to hook a different compile
+        method in.
+
+        .. versionadded:: 2.5
+        """
+        return compile(source, filename, 'exec')
+
+    @internalcode
+    def compile(self, source, name=None, filename=None, raw=False,
+                defer_init=False):
+        """Compile a node or template source code.  The `name` parameter is
+        the load name of the template after it was joined using
+        :meth:`join_path` if necessary, not the filename on the file system.
+        the `filename` parameter is the estimated filename of the template on
+        the file system.  If the template came from a database or memory this
+        can be omitted.
+
+        The return value of this method is a python code object.  If the `raw`
+        parameter is `True` the return value will be a string with python
+        code equivalent to the bytecode returned otherwise.  This method is
+        mainly used internally.
+
+        `defer_init` is use internally to aid the module code generator.  This
+        causes the generated code to be able to import without the global
+        environment variable to be set.
+
+        .. versionadded:: 2.4
+           `defer_init` parameter added.
+        """
+        source_hint = None
+        try:
+            if isinstance(source, string_types):
+                source_hint = source
+                source = self._parse(source, name, filename)
+            source = self._generate(source, name, filename,
+                                    defer_init=defer_init)
+            if raw:
+                return source
+            if filename is None:
+                filename = '<template>'
+            else:
+                filename = encode_filename(filename)
+            return self._compile(source, filename)
+        except TemplateSyntaxError:
+            self.handle_exception(source=source_hint)
+
+    def compile_expression(self, source, undefined_to_none=True):
+        """A handy helper method that returns a callable that accepts keyword
+        arguments that appear as variables in the expression.  If called it
+        returns the result of the expression.
+
+        This is useful if applications want to use the same rules as Jinja
+        in template "configuration files" or similar situations.
+
+        Example usage:
+
+        >>> env = Environment()
+        >>> expr = env.compile_expression('foo == 42')
+        >>> expr(foo=23)
+        False
+        >>> expr(foo=42)
+        True
+
+        Per default the return value is converted to `None` if the
+        expression returns an undefined value.  This can be changed
+        by setting `undefined_to_none` to `False`.
+
+        >>> env.compile_expression('var')() is None
+        True
+        >>> env.compile_expression('var', undefined_to_none=False)()
+        Undefined
+
+        .. versionadded:: 2.1
+        """
+        parser = Parser(self, source, state='variable')
+        try:
+            expr = parser.parse_expression()
+            if not parser.stream.eos:
+                raise TemplateSyntaxError('chunk after expression',
+                                          parser.stream.current.lineno,
+                                          None, None)
+            expr.set_environment(self)
+        except TemplateSyntaxError:
+            if sys.exc_info() is not None:
+                self.handle_exception(source=source)
+
+        body = [nodes.Assign(nodes.Name('result', 'store'), expr, lineno=1)]
+        template = self.from_string(nodes.Template(body, lineno=1))
+        return TemplateExpression(template, undefined_to_none)
+
+    def compile_templates(self, target, extensions=None, filter_func=None,
+                          zip='deflated', log_function=None,
+                          ignore_errors=True, py_compile=False):
+        """Finds all the templates the loader can find, compiles them
+        and stores them in `target`.  If `zip` is `None`, instead of in a
+        zipfile, the templates will be stored in a directory.
+        By default a deflate zip algorithm is used. To switch to
+        the stored algorithm, `zip` can be set to ``'stored'``.
+
+        `extensions` and `filter_func` are passed to :meth:`list_templates`.
+        Each template returned will be compiled to the target folder or
+        zipfile.
+
+        By default template compilation errors are ignored.  In case a
+        log function is provided, errors are logged.  If you want template
+        syntax errors to abort the compilation you can set `ignore_errors`
+        to `False` and you will get an exception on syntax errors.
+
+        If `py_compile` is set to `True` .pyc files will be written to the
+        target instead of standard .py files.  This flag does not do anything
+        on pypy and Python 3 where pyc files are not picked up by itself and
+        don't give much benefit.
+
+        .. versionadded:: 2.4
+        """
+        from jinja2.loaders import ModuleLoader
+
+        if log_function is None:
+            log_function = lambda x: None
+
+        if py_compile:
+            if not PY2 or PYPY:
+                from warnings import warn
+                warn(Warning('py_compile has no effect on pypy or Python 3'))
+                py_compile = False
+            else:
+                import imp
+                import marshal
+                py_header = imp.get_magic() + \
+                    u'\xff\xff\xff\xff'.encode('iso-8859-15')
+
+                # Python 3.3 added a source filesize to the header
+                if sys.version_info >= (3, 3):
+                    py_header += u'\x00\x00\x00\x00'.encode('iso-8859-15')
+
+        def write_file(filename, data):
+            if zip:
+                info = ZipInfo(filename)
+                info.external_attr = 0o755 << 16
+                zip_file.writestr(info, data)
+            else:
+                if isinstance(data, text_type):
+                    data = data.encode("utf8")
+
+                with open(os.path.join(target, filename), "wb") as f:
+                    f.write(data)
+
+        if zip is not None:
+            from zipfile import ZipFile, ZipInfo, ZIP_DEFLATED, ZIP_STORED
+            zip_file = ZipFile(target, 'w', dict(deflated=ZIP_DEFLATED,
+                                                 stored=ZIP_STORED)[zip])
+            log_function('Compiling into Zip archive "%s"' % target)
+        else:
+            if not os.path.isdir(target):
+                os.makedirs(target)
+            log_function('Compiling into folder "%s"' % target)
+
+        try:
+            for name in self.list_templates(extensions, filter_func):
+                source, filename, _ = self.loader.get_source(self, name)
+                try:
+                    code = self.compile(source, name, filename, True, True)
+                except TemplateSyntaxError as e:
+                    if not ignore_errors:
+                        raise
+                    log_function('Could not compile "%s": %s' % (name, e))
+                    continue
+
+                filename = ModuleLoader.get_module_filename(name)
+
+                if py_compile:
+                    c = self._compile(code, encode_filename(filename))
+                    write_file(filename + 'c', py_header +
+                               marshal.dumps(c))
+                    log_function('Byte-compiled "%s" as %s' %
+                                 (name, filename + 'c'))
+                else:
+                    write_file(filename, code)
+                    log_function('Compiled "%s" as %s' % (name, filename))
+        finally:
+            if zip:
+                zip_file.close()
+
+        log_function('Finished compiling templates')
+
+    def list_templates(self, extensions=None, filter_func=None):
+        """Returns a list of templates for this environment.  This requires
+        that the loader supports the loader's
+        :meth:`~BaseLoader.list_templates` method.
+
+        If there are other files in the template folder besides the
+        actual templates, the returned list can be filtered.  There are two
+        ways: either `extensions` is set to a list of file extensions for
+        templates, or a `filter_func` can be provided which is a callable that
+        is passed a template name and should return `True` if it should end up
+        in the result list.
+
+        If the loader does not support that, a :exc:`TypeError` is raised.
+
+        .. versionadded:: 2.4
+        """
+        x = self.loader.list_templates()
+        if extensions is not None:
+            if filter_func is not None:
+                raise TypeError('either extensions or filter_func '
+                                'can be passed, but not both')
+            filter_func = lambda x: '.' in x and \
+                                    x.rsplit('.', 1)[1] in extensions
+        if filter_func is not None:
+            x = list(ifilter(filter_func, x))
+        return x
+
+    def handle_exception(self, source=None):
+        """Exception handling helper.  This is used internally to either raise
+        rewritten exceptions or return a rendered traceback for the template.
+        """
+        from jinja2.debug import rewrite_traceback_stack
+        reraise(*rewrite_traceback_stack(source=source))
+
+    def join_path(self, template, parent):
+        """Join a template with the parent.  By default all the lookups are
+        relative to the loader root so this method returns the `template`
+        parameter unchanged, but if the paths should be relative to the
+        parent template, this function can be used to calculate the real
+        template name.
+
+        Subclasses may override this method and implement template path
+        joining here.
+        """
+        return template
+
+    @internalcode
+    def _load_template(self, name, globals):
+        if self.loader is None:
+            raise TypeError('no loader for this environment specified')
+        cache_key = (weakref.ref(self.loader), name)
+        if self.cache is not None:
+            template = self.cache.get(cache_key)
+            if template is not None and (not self.auto_reload or
+                                         template.is_up_to_date):
+                return template
+        template = self.loader.load(self, name, globals)
+        if self.cache is not None:
+            self.cache[cache_key] = template
+        return template
+
+    @internalcode
+    def get_template(self, name, parent=None, globals=None):
+        """Load a template from the loader.  If a loader is configured this
+        method asks the loader for the template and returns a :class:`Template`.
+        If the `parent` parameter is not `None`, :meth:`join_path` is called
+        to get the real template name before loading.
+
+        The `globals` parameter can be used to provide template wide globals.
+        These variables are available in the context at render time.
+
+        If the template does not exist a :exc:`TemplateNotFound` exception is
+        raised.
+
+        .. versionchanged:: 2.4
+           If `name` is a :class:`Template` object it is returned from the
+           function unchanged.
+        """
+        if isinstance(name, Template):
+            return name
+        if parent is not None:
+            name = self.join_path(name, parent)
+        return self._load_template(name, self.make_globals(globals))
+
+    @internalcode
+    def select_template(self, names, parent=None, globals=None):
+        """Works like :meth:`get_template` but tries a number of templates
+        before it fails.  If it cannot find any of the templates, it will
+        raise a :exc:`TemplatesNotFound` exception.
+
+        .. versionchanged:: 2.11
+            If names is :class:`Undefined`, an :exc:`UndefinedError` is
+            raised instead. If no templates were found and names
+            contains :class:`Undefined`, the message is more helpful.
+
+        .. versionchanged:: 2.4
+           If `names` contains a :class:`Template` object it is returned
+           from the function unchanged.
+
+        .. versionadded:: 2.3
+        """
+        if isinstance(names, Undefined):
+            names._fail_with_undefined_error()
+
+        if not names:
+            raise TemplatesNotFound(message=u'Tried to select from an empty list '
+                                            u'of templates.')
+        globals = self.make_globals(globals)
+        for name in names:
+            if isinstance(name, Template):
+                return name
+            if parent is not None:
+                name = self.join_path(name, parent)
+            try:
+                return self._load_template(name, globals)
+            except (TemplateNotFound, UndefinedError):
+                pass
+        raise TemplatesNotFound(names)
+
+    @internalcode
+    def get_or_select_template(self, template_name_or_list,
+                               parent=None, globals=None):
+        """Does a typecheck and dispatches to :meth:`select_template`
+        if an iterable of template names is given, otherwise to
+        :meth:`get_template`.
+
+        .. versionadded:: 2.3
+        """
+        if isinstance(template_name_or_list, (string_types, Undefined)):
+            return self.get_template(template_name_or_list, parent, globals)
+        elif isinstance(template_name_or_list, Template):
+            return template_name_or_list
+        return self.select_template(template_name_or_list, parent, globals)
+
+    def from_string(self, source, globals=None, template_class=None):
+        """Load a template from a string.  This parses the source given and
+        returns a :class:`Template` object.
+        """
+        globals = self.make_globals(globals)
+        cls = template_class or self.template_class
+        return cls.from_code(self, self.compile(source), globals, None)
+
+    def make_globals(self, d):
+        """Return a dict for the globals."""
+        if not d:
+            return self.globals
+        return dict(self.globals, **d)
+
+
+class Template(object):
+    """The central template object.  This class represents a compiled template
+    and is used to evaluate it.
+
+    Normally the template object is generated from an :class:`Environment` but
+    it also has a constructor that makes it possible to create a template
+    instance directly using the constructor.  It takes the same arguments as
+    the environment constructor but it's not possible to specify a loader.
+
+    Every template object has a few methods and members that are guaranteed
+    to exist.  However it's important that a template object should be
+    considered immutable.  Modifications on the object are not supported.
+
+    Template objects created from the constructor rather than an environment
+    do have an `environment` attribute that points to a temporary environment
+    that is probably shared with other templates created with the constructor
+    and compatible settings.
+
+    >>> template = Template('Hello {{ name }}!')
+    >>> template.render(name='John Doe') == u'Hello John Doe!'
+    True
+    >>> stream = template.stream(name='John Doe')
+    >>> next(stream) == u'Hello John Doe!'
+    True
+    >>> next(stream)
+    Traceback (most recent call last):
+        ...
+    StopIteration
+    """
+
+    #: Type of environment to create when creating a template directly
+    #: rather than through an existing environment.
+    environment_class = Environment
+
+    def __new__(cls, source,
+                block_start_string=BLOCK_START_STRING,
+                block_end_string=BLOCK_END_STRING,
+                variable_start_string=VARIABLE_START_STRING,
+                variable_end_string=VARIABLE_END_STRING,
+                comment_start_string=COMMENT_START_STRING,
+                comment_end_string=COMMENT_END_STRING,
+                line_statement_prefix=LINE_STATEMENT_PREFIX,
+                line_comment_prefix=LINE_COMMENT_PREFIX,
+                trim_blocks=TRIM_BLOCKS,
+                lstrip_blocks=LSTRIP_BLOCKS,
+                newline_sequence=NEWLINE_SEQUENCE,
+                keep_trailing_newline=KEEP_TRAILING_NEWLINE,
+                extensions=(),
+                optimized=True,
+                undefined=Undefined,
+                finalize=None,
+                autoescape=False,
+                enable_async=False):
+        env = get_spontaneous_environment(
+            cls.environment_class,
+            block_start_string, block_end_string, variable_start_string,
+            variable_end_string, comment_start_string, comment_end_string,
+            line_statement_prefix, line_comment_prefix, trim_blocks,
+            lstrip_blocks, newline_sequence, keep_trailing_newline,
+            frozenset(extensions), optimized, undefined, finalize, autoescape,
+            None, 0, False, None, enable_async)
+        return env.from_string(source, template_class=cls)
+
+    @classmethod
+    def from_code(cls, environment, code, globals, uptodate=None):
+        """Creates a template object from compiled code and the globals.  This
+        is used by the loaders and environment to create a template object.
+        """
+        namespace = {
+            'environment':  environment,
+            '__file__':     code.co_filename
+        }
+        exec(code, namespace)
+        rv = cls._from_namespace(environment, namespace, globals)
+        rv._uptodate = uptodate
+        return rv
+
+    @classmethod
+    def from_module_dict(cls, environment, module_dict, globals):
+        """Creates a template object from a module.  This is used by the
+        module loader to create a template object.
+
+        .. versionadded:: 2.4
+        """
+        return cls._from_namespace(environment, module_dict, globals)
+
+    @classmethod
+    def _from_namespace(cls, environment, namespace, globals):
+        t = object.__new__(cls)
+        t.environment = environment
+        t.globals = globals
+        t.name = namespace['name']
+        t.filename = namespace['__file__']
+        t.blocks = namespace['blocks']
+
+        # render function and module
+        t.root_render_func = namespace['root']
+        t._module = None
+
+        # debug and loader helpers
+        t._debug_info = namespace['debug_info']
+        t._uptodate = None
+
+        # store the reference
+        namespace['environment'] = environment
+        namespace['__jinja_template__'] = t
+
+        return t
+
+    def render(self, *args, **kwargs):
+        """This method accepts the same arguments as the `dict` constructor:
+        A dict, a dict subclass or some keyword arguments.  If no arguments
+        are given the context will be empty.  These two calls do the same::
+
+            template.render(knights='that say nih')
+            template.render({'knights': 'that say nih'})
+
+        This will return the rendered template as unicode string.
+        """
+        vars = dict(*args, **kwargs)
+        try:
+            return concat(self.root_render_func(self.new_context(vars)))
+        except Exception:
+            self.environment.handle_exception()
+
+    def render_async(self, *args, **kwargs):
+        """This works similar to :meth:`render` but returns a coroutine
+        that when awaited returns the entire rendered template string.  This
+        requires the async feature to be enabled.
+
+        Example usage::
+
+            await template.render_async(knights='that say nih; asynchronously')
+        """
+        # see asyncsupport for the actual implementation
+        raise NotImplementedError('This feature is not available for this '
+                                  'version of Python')
+
+    def stream(self, *args, **kwargs):
+        """Works exactly like :meth:`generate` but returns a
+        :class:`TemplateStream`.
+        """
+        return TemplateStream(self.generate(*args, **kwargs))
+
+    def generate(self, *args, **kwargs):
+        """For very large templates it can be useful to not render the whole
+        template at once but evaluate each statement after another and yield
+        piece for piece.  This method basically does exactly that and returns
+        a generator that yields one item after another as unicode strings.
+
+        It accepts the same arguments as :meth:`render`.
+        """
+        vars = dict(*args, **kwargs)
+        try:
+            for event in self.root_render_func(self.new_context(vars)):
+                yield event
+        except Exception:
+            yield self.environment.handle_exception()
+
+    def generate_async(self, *args, **kwargs):
+        """An async version of :meth:`generate`.  Works very similarly but
+        returns an async iterator instead.
+        """
+        # see asyncsupport for the actual implementation
+        raise NotImplementedError('This feature is not available for this '
+                                  'version of Python')
+
+    def new_context(self, vars=None, shared=False, locals=None):
+        """Create a new :class:`Context` for this template.  The vars
+        provided will be passed to the template.  Per default the globals
+        are added to the context.  If shared is set to `True` the data
+        is passed as is to the context without adding the globals.
+
+        `locals` can be a dict of local variables for internal usage.
+        """
+        return new_context(self.environment, self.name, self.blocks,
+                           vars, shared, self.globals, locals)
+
+    def make_module(self, vars=None, shared=False, locals=None):
+        """This method works like the :attr:`module` attribute when called
+        without arguments but it will evaluate the template on every call
+        rather than caching it.  It's also possible to provide
+        a dict which is then used as context.  The arguments are the same
+        as for the :meth:`new_context` method.
+        """
+        return TemplateModule(self, self.new_context(vars, shared, locals))
+
+    def make_module_async(self, vars=None, shared=False, locals=None):
+        """As template module creation can invoke template code for
+        asynchronous executions this method must be used instead of the
+        normal :meth:`make_module` one.  Likewise the module attribute
+        becomes unavailable in async mode.
+        """
+        # see asyncsupport for the actual implementation
+        raise NotImplementedError('This feature is not available for this '
+                                  'version of Python')
+
+    @internalcode
+    def _get_default_module(self):
+        if self._module is not None:
+            return self._module
+        self._module = rv = self.make_module()
+        return rv
+
+    @property
+    def module(self):
+        """The template as module.  This is used for imports in the
+        template runtime but is also useful if one wants to access
+        exported template variables from the Python layer:
+
+        >>> t = Template('{% macro foo() %}42{% endmacro %}23')
+        >>> str(t.module)
+        '23'
+        >>> t.module.foo() == u'42'
+        True
+
+        This attribute is not available if async mode is enabled.
+        """
+        return self._get_default_module()
+
+    def get_corresponding_lineno(self, lineno):
+        """Return the source line number of a line number in the
+        generated bytecode as they are not in sync.
+        """
+        for template_line, code_line in reversed(self.debug_info):
+            if code_line <= lineno:
+                return template_line
+        return 1
+
+    @property
+    def is_up_to_date(self):
+        """If this variable is `False` there is a newer version available."""
+        if self._uptodate is None:
+            return True
+        return self._uptodate()
+
+    @property
+    def debug_info(self):
+        """The debug info mapping."""
+        if self._debug_info:
+            return [tuple(imap(int, x.split('='))) for x in
+                    self._debug_info.split('&')]
+        return []
+
+    def __repr__(self):
+        if self.name is None:
+            name = 'memory:%x' % id(self)
+        else:
+            name = repr(self.name)
+        return '<%s %s>' % (self.__class__.__name__, name)
+
+
+@implements_to_string
+class TemplateModule(object):
+    """Represents an imported template.  All the exported names of the
+    template are available as attributes on this object.  Additionally
+    converting it into an unicode- or bytestrings renders the contents.
+    """
+
+    def __init__(self, template, context, body_stream=None):
+        if body_stream is None:
+            if context.environment.is_async:
+                raise RuntimeError('Async mode requires a body stream '
+                                   'to be passed to a template module.  Use '
+                                   'the async methods of the API you are '
+                                   'using.')
+            body_stream = list(template.root_render_func(context))
+        self._body_stream = body_stream
+        self.__dict__.update(context.get_exported())
+        self.__name__ = template.name
+
+    def __html__(self):
+        return Markup(concat(self._body_stream))
+
+    def __str__(self):
+        return concat(self._body_stream)
+
+    def __repr__(self):
+        if self.__name__ is None:
+            name = 'memory:%x' % id(self)
+        else:
+            name = repr(self.__name__)
+        return '<%s %s>' % (self.__class__.__name__, name)
+
+
+class TemplateExpression(object):
+    """The :meth:`jinja2.Environment.compile_expression` method returns an
+    instance of this object.  It encapsulates the expression-like access
+    to the template with an expression it wraps.
+    """
+
+    def __init__(self, template, undefined_to_none):
+        self._template = template
+        self._undefined_to_none = undefined_to_none
+
+    def __call__(self, *args, **kwargs):
+        context = self._template.new_context(dict(*args, **kwargs))
+        consume(self._template.root_render_func(context))
+        rv = context.vars['result']
+        if self._undefined_to_none and isinstance(rv, Undefined):
+            rv = None
+        return rv
+
+
+@implements_iterator
+class TemplateStream(object):
+    """A template stream works pretty much like an ordinary python generator
+    but it can buffer multiple items to reduce the number of total iterations.
+    Per default the output is unbuffered which means that for every unbuffered
+    instruction in the template one unicode string is yielded.
+
+    If buffering is enabled with a buffer size of 5, five items are combined
+    into a new unicode string.  This is mainly useful if you are streaming
+    big templates to a client via WSGI which flushes after each iteration.
+    """
+
+    def __init__(self, gen):
+        self._gen = gen
+        self.disable_buffering()
+
+    def dump(self, fp, encoding=None, errors='strict'):
+        """Dump the complete stream into a file or file-like object.
+        Per default unicode strings are written, if you want to encode
+        before writing specify an `encoding`.
+
+        Example usage::
+
+            Template('Hello {{ name }}!').stream(name='foo').dump('hello.html')
+        """
+        close = False
+        if isinstance(fp, string_types):
+            if encoding is None:
+                encoding = 'utf-8'
+            fp = open(fp, 'wb')
+            close = True
+        try:
+            if encoding is not None:
+                iterable = (x.encode(encoding, errors) for x in self)
+            else:
+                iterable = self
+            if hasattr(fp, 'writelines'):
+                fp.writelines(iterable)
+            else:
+                for item in iterable:
+                    fp.write(item)
+        finally:
+            if close:
+                fp.close()
+
+    def disable_buffering(self):
+        """Disable the output buffering."""
+        self._next = partial(next, self._gen)
+        self.buffered = False
+
+    def _buffered_generator(self, size):
+        buf = []
+        c_size = 0
+        push = buf.append
+
+        while 1:
+            try:
+                while c_size < size:
+                    c = next(self._gen)
+                    push(c)
+                    if c:
+                        c_size += 1
+            except StopIteration:
+                if not c_size:
+                    return
+            yield concat(buf)
+            del buf[:]
+            c_size = 0
+
+    def enable_buffering(self, size=5):
+        """Enable buffering.  Buffer `size` items before yielding them."""
+        if size <= 1:
+            raise ValueError('buffer size too small')
+
+        self.buffered = True
+        self._next = partial(next, self._buffered_generator(size))
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        return self._next()
+
+
+# hook in default template class.  if anyone reads this comment: ignore that
+# it's possible to use custom templates ;-)
+Environment.template_class = Template
diff --git a/src/jinja2/exceptions.py b/src/jinja2/exceptions.py
new file mode 100644
index 0000000..c01483b
--- /dev/null
+++ b/src/jinja2/exceptions.py
@@ -0,0 +1,179 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.exceptions
+    ~~~~~~~~~~~~~~~~~
+
+    Jinja exceptions.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+from jinja2._compat import imap, text_type, PY2, implements_to_string
+
+
+class TemplateError(Exception):
+    """Baseclass for all template errors."""
+
+    if PY2:
+        def __init__(self, message=None):
+            if message is not None:
+                message = text_type(message).encode('utf-8')
+            Exception.__init__(self, message)
+
+        @property
+        def message(self):
+            if self.args:
+                message = self.args[0]
+                if message is not None:
+                    return message.decode('utf-8', 'replace')
+
+        def __unicode__(self):
+            return self.message or u''
+    else:
+        def __init__(self, message=None):
+            Exception.__init__(self, message)
+
+        @property
+        def message(self):
+            if self.args:
+                message = self.args[0]
+                if message is not None:
+                    return message
+
+
+@implements_to_string
+class TemplateNotFound(IOError, LookupError, TemplateError):
+    """Raised if a template does not exist.
+
+    .. versionchanged:: 2.11
+        If the given name is :class:`Undefined` and no message was
+        provided, an :exc:`UndefinedError` is raised.
+    """
+
+    # looks weird, but removes the warning descriptor that just
+    # bogusly warns us about message being deprecated
+    message = None
+
+    def __init__(self, name, message=None):
+        IOError.__init__(self, name)
+
+        if message is None:
+            from jinja2.runtime import Undefined
+
+            if isinstance(name, Undefined):
+                name._fail_with_undefined_error()
+
+            message = name
+
+        self.message = message
+        self.name = name
+        self.templates = [name]
+
+    def __str__(self):
+        return self.message
+
+
+class TemplatesNotFound(TemplateNotFound):
+    """Like :class:`TemplateNotFound` but raised if multiple templates
+    are selected.  This is a subclass of :class:`TemplateNotFound`
+    exception, so just catching the base exception will catch both.
+
+    .. versionchanged:: 2.11
+        If a name in the list of names is :class:`Undefined`, a message
+        about it being undefined is shown rather than the empty string.
+
+    .. versionadded:: 2.2
+    """
+
+    def __init__(self, names=(), message=None):
+        if message is None:
+            from jinja2.runtime import Undefined
+
+            parts = []
+
+            for name in names:
+                if isinstance(name, Undefined):
+                    parts.append(name._undefined_message)
+                else:
+                    parts.append(name)
+
+            message = u'none of the templates given were found: ' + \
+                      u', '.join(imap(text_type, parts))
+        TemplateNotFound.__init__(self, names and names[-1] or None, message)
+        self.templates = list(names)
+
+
+@implements_to_string
+class TemplateSyntaxError(TemplateError):
+    """Raised to tell the user that there is a problem with the template."""
+
+    def __init__(self, message, lineno, name=None, filename=None):
+        TemplateError.__init__(self, message)
+        self.lineno = lineno
+        self.name = name
+        self.filename = filename
+        self.source = None
+
+        # this is set to True if the debug.translate_syntax_error
+        # function translated the syntax error into a new traceback
+        self.translated = False
+
+    def __str__(self):
+        # for translated errors we only return the message
+        if self.translated:
+            return self.message
+
+        # otherwise attach some stuff
+        location = 'line %d' % self.lineno
+        name = self.filename or self.name
+        if name:
+            location = 'File "%s", %s' % (name, location)
+        lines = [self.message, '  ' + location]
+
+        # if the source is set, add the line to the output
+        if self.source is not None:
+            try:
+                line = self.source.splitlines()[self.lineno - 1]
+            except IndexError:
+                line = None
+            if line:
+                lines.append('    ' + line.strip())
+
+        return u'\n'.join(lines)
+
+    def __reduce__(self):
+        # https://bugs.python.org/issue1692335 Exceptions that take
+        # multiple required arguments have problems with pickling.
+        # Without this, raises TypeError: __init__() missing 1 required
+        # positional argument: 'lineno'
+        return self.__class__, (self.message, self.lineno, self.name, self.filename)
+
+
+class TemplateAssertionError(TemplateSyntaxError):
+    """Like a template syntax error, but covers cases where something in the
+    template caused an error at compile time that wasn't necessarily caused
+    by a syntax error.  However it's a direct subclass of
+    :exc:`TemplateSyntaxError` and has the same attributes.
+    """
+
+
+class TemplateRuntimeError(TemplateError):
+    """A generic runtime error in the template engine.  Under some situations
+    Jinja may raise this exception.
+    """
+
+
+class UndefinedError(TemplateRuntimeError):
+    """Raised if a template tries to operate on :class:`Undefined`."""
+
+
+class SecurityError(TemplateRuntimeError):
+    """Raised if a template tries to do something insecure if the
+    sandbox is enabled.
+    """
+
+
+class FilterArgumentError(TemplateRuntimeError):
+    """This error is raised if a filter was called with inappropriate
+    arguments
+    """
diff --git a/src/jinja2/ext.py b/src/jinja2/ext.py
new file mode 100644
index 0000000..f04b37b
--- /dev/null
+++ b/src/jinja2/ext.py
@@ -0,0 +1,682 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.ext
+    ~~~~~~~~~~
+
+    Jinja extensions allow adding custom tags and behavior. The
+    following extensions are included:
+
+    -   An 18n support ``{% trans %}`` tag.
+    -   A ``{% do %}`` tag.
+    -   Loop control ``{% break %}`` and ``{% continue %}`` tags.
+    -   A ``{% debug %}`` tag.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+import pprint
+import re
+from sys import version_info
+
+from jinja2 import nodes
+from jinja2.defaults import BLOCK_START_STRING, \
+     BLOCK_END_STRING, VARIABLE_START_STRING, VARIABLE_END_STRING, \
+     COMMENT_START_STRING, COMMENT_END_STRING, LINE_STATEMENT_PREFIX, \
+     LINE_COMMENT_PREFIX, TRIM_BLOCKS, NEWLINE_SEQUENCE, \
+     KEEP_TRAILING_NEWLINE, LSTRIP_BLOCKS
+from jinja2.environment import Environment
+from jinja2.nodes import ContextReference
+from jinja2.runtime import concat
+from jinja2.exceptions import TemplateAssertionError, TemplateSyntaxError
+from jinja2.utils import contextfunction, import_string, Markup
+from jinja2._compat import with_metaclass, string_types, iteritems
+from markupsafe import escape
+
+
+# the only real useful gettext functions for a Jinja template.  Note
+# that ugettext must be assigned to gettext as Jinja doesn't support
+# non unicode strings.
+GETTEXT_FUNCTIONS = ('_', 'gettext', 'ngettext')
+
+
+class ExtensionRegistry(type):
+    """Gives the extension an unique identifier."""
+
+    def __new__(cls, name, bases, d):
+        rv = type.__new__(cls, name, bases, d)
+        rv.identifier = rv.__module__ + '.' + rv.__name__
+        return rv
+
+
+class Extension(with_metaclass(ExtensionRegistry, object)):
+    """Extensions can be used to add extra functionality to the Jinja template
+    system at the parser level.  Custom extensions are bound to an environment
+    but may not store environment specific data on `self`.  The reason for
+    this is that an extension can be bound to another environment (for
+    overlays) by creating a copy and reassigning the `environment` attribute.
+
+    As extensions are created by the environment they cannot accept any
+    arguments for configuration.  One may want to work around that by using
+    a factory function, but that is not possible as extensions are identified
+    by their import name.  The correct way to configure the extension is
+    storing the configuration values on the environment.  Because this way the
+    environment ends up acting as central configuration storage the
+    attributes may clash which is why extensions have to ensure that the names
+    they choose for configuration are not too generic.  ``prefix`` for example
+    is a terrible name, ``fragment_cache_prefix`` on the other hand is a good
+    name as includes the name of the extension (fragment cache).
+    """
+
+    #: if this extension parses this is the list of tags it's listening to.
+    tags = set()
+
+    #: the priority of that extension.  This is especially useful for
+    #: extensions that preprocess values.  A lower value means higher
+    #: priority.
+    #:
+    #: .. versionadded:: 2.4
+    priority = 100
+
+    def __init__(self, environment):
+        self.environment = environment
+
+    def bind(self, environment):
+        """Create a copy of this extension bound to another environment."""
+        rv = object.__new__(self.__class__)
+        rv.__dict__.update(self.__dict__)
+        rv.environment = environment
+        return rv
+
+    def preprocess(self, source, name, filename=None):
+        """This method is called before the actual lexing and can be used to
+        preprocess the source.  The `filename` is optional.  The return value
+        must be the preprocessed source.
+        """
+        return source
+
+    def filter_stream(self, stream):
+        """It's passed a :class:`~jinja2.lexer.TokenStream` that can be used
+        to filter tokens returned.  This method has to return an iterable of
+        :class:`~jinja2.lexer.Token`\\s, but it doesn't have to return a
+        :class:`~jinja2.lexer.TokenStream`.
+
+        In the `ext` folder of the Jinja source distribution there is a file
+        called `inlinegettext.py` which implements a filter that utilizes this
+        method.
+        """
+        return stream
+
+    def parse(self, parser):
+        """If any of the :attr:`tags` matched this method is called with the
+        parser as first argument.  The token the parser stream is pointing at
+        is the name token that matched.  This method has to return one or a
+        list of multiple nodes.
+        """
+        raise NotImplementedError()
+
+    def attr(self, name, lineno=None):
+        """Return an attribute node for the current extension.  This is useful
+        to pass constants on extensions to generated template code.
+
+        ::
+
+            self.attr('_my_attribute', lineno=lineno)
+        """
+        return nodes.ExtensionAttribute(self.identifier, name, lineno=lineno)
+
+    def call_method(self, name, args=None, kwargs=None, dyn_args=None,
+                    dyn_kwargs=None, lineno=None):
+        """Call a method of the extension.  This is a shortcut for
+        :meth:`attr` + :class:`jinja2.nodes.Call`.
+        """
+        if args is None:
+            args = []
+        if kwargs is None:
+            kwargs = []
+        return nodes.Call(self.attr(name, lineno=lineno), args, kwargs,
+                          dyn_args, dyn_kwargs, lineno=lineno)
+
+
+@contextfunction
+def _gettext_alias(__context, *args, **kwargs):
+    return __context.call(__context.resolve('gettext'), *args, **kwargs)
+
+
+def _make_new_gettext(func):
+    @contextfunction
+    def gettext(__context, __string, **variables):
+        rv = __context.call(func, __string)
+        if __context.eval_ctx.autoescape:
+            rv = Markup(rv)
+        # Always treat as a format string, even if there are no
+        # variables. This makes translation strings more consistent
+        # and predictable. This requires escaping
+        return rv % variables
+    return gettext
+
+
+def _make_new_ngettext(func):
+    @contextfunction
+    def ngettext(__context, __singular, __plural, __num, **variables):
+        variables.setdefault('num', __num)
+        rv = __context.call(func, __singular, __plural, __num)
+        if __context.eval_ctx.autoescape:
+            rv = Markup(rv)
+        # Always treat as a format string, see gettext comment above.
+        return rv % variables
+    return ngettext
+
+
+class InternationalizationExtension(Extension):
+    """This extension adds gettext support to Jinja."""
+    tags = {'trans'}
+
+    # TODO: the i18n extension is currently reevaluating values in a few
+    # situations.  Take this example:
+    #   {% trans count=something() %}{{ count }} foo{% pluralize
+    #     %}{{ count }} fooss{% endtrans %}
+    # something is called twice here.  One time for the gettext value and
+    # the other time for the n-parameter of the ngettext function.
+
+    def __init__(self, environment):
+        Extension.__init__(self, environment)
+        environment.globals['_'] = _gettext_alias
+        environment.extend(
+            install_gettext_translations=self._install,
+            install_null_translations=self._install_null,
+            install_gettext_callables=self._install_callables,
+            uninstall_gettext_translations=self._uninstall,
+            extract_translations=self._extract,
+            newstyle_gettext=False
+        )
+
+    def _install(self, translations, newstyle=None):
+        gettext = getattr(translations, 'ugettext', None)
+        if gettext is None:
+            gettext = translations.gettext
+        ngettext = getattr(translations, 'ungettext', None)
+        if ngettext is None:
+            ngettext = translations.ngettext
+        self._install_callables(gettext, ngettext, newstyle)
+
+    def _install_null(self, newstyle=None):
+        self._install_callables(
+            lambda x: x,
+            lambda s, p, n: (n != 1 and (p,) or (s,))[0],
+            newstyle
+        )
+
+    def _install_callables(self, gettext, ngettext, newstyle=None):
+        if newstyle is not None:
+            self.environment.newstyle_gettext = newstyle
+        if self.environment.newstyle_gettext:
+            gettext = _make_new_gettext(gettext)
+            ngettext = _make_new_ngettext(ngettext)
+        self.environment.globals.update(
+            gettext=gettext,
+            ngettext=ngettext
+        )
+
+    def _uninstall(self, translations):
+        for key in 'gettext', 'ngettext':
+            self.environment.globals.pop(key, None)
+
+    def _extract(self, source, gettext_functions=GETTEXT_FUNCTIONS):
+        if isinstance(source, string_types):
+            source = self.environment.parse(source)
+        return extract_from_ast(source, gettext_functions)
+
+    def parse(self, parser):
+        """Parse a translatable tag."""
+        lineno = next(parser.stream).lineno
+        num_called_num = False
+
+        # find all the variables referenced.  Additionally a variable can be
+        # defined in the body of the trans block too, but this is checked at
+        # a later state.
+        plural_expr = None
+        plural_expr_assignment = None
+        variables = {}
+        trimmed = None
+        while parser.stream.current.type != 'block_end':
+            if variables:
+                parser.stream.expect('comma')
+
+            # skip colon for python compatibility
+            if parser.stream.skip_if('colon'):
+                break
+
+            name = parser.stream.expect('name')
+            if name.value in variables:
+                parser.fail('translatable variable %r defined twice.' %
+                            name.value, name.lineno,
+                            exc=TemplateAssertionError)
+
+            # expressions
+            if parser.stream.current.type == 'assign':
+                next(parser.stream)
+                variables[name.value] = var = parser.parse_expression()
+            elif trimmed is None and name.value in ('trimmed', 'notrimmed'):
+                trimmed = name.value == 'trimmed'
+                continue
+            else:
+                variables[name.value] = var = nodes.Name(name.value, 'load')
+
+            if plural_expr is None:
+                if isinstance(var, nodes.Call):
+                    plural_expr = nodes.Name('_trans', 'load')
+                    variables[name.value] = plural_expr
+                    plural_expr_assignment = nodes.Assign(
+                        nodes.Name('_trans', 'store'), var)
+                else:
+                    plural_expr = var
+                num_called_num = name.value == 'num'
+
+        parser.stream.expect('block_end')
+
+        plural = None
+        have_plural = False
+        referenced = set()
+
+        # now parse until endtrans or pluralize
+        singular_names, singular = self._parse_block(parser, True)
+        if singular_names:
+            referenced.update(singular_names)
+            if plural_expr is None:
+                plural_expr = nodes.Name(singular_names[0], 'load')
+                num_called_num = singular_names[0] == 'num'
+
+        # if we have a pluralize block, we parse that too
+        if parser.stream.current.test('name:pluralize'):
+            have_plural = True
+            next(parser.stream)
+            if parser.stream.current.type != 'block_end':
+                name = parser.stream.expect('name')
+                if name.value not in variables:
+                    parser.fail('unknown variable %r for pluralization' %
+                                name.value, name.lineno,
+                                exc=TemplateAssertionError)
+                plural_expr = variables[name.value]
+                num_called_num = name.value == 'num'
+            parser.stream.expect('block_end')
+            plural_names, plural = self._parse_block(parser, False)
+            next(parser.stream)
+            referenced.update(plural_names)
+        else:
+            next(parser.stream)
+
+        # register free names as simple name expressions
+        for var in referenced:
+            if var not in variables:
+                variables[var] = nodes.Name(var, 'load')
+
+        if not have_plural:
+            plural_expr = None
+        elif plural_expr is None:
+            parser.fail('pluralize without variables', lineno)
+
+        if trimmed is None:
+            trimmed = self.environment.policies['ext.i18n.trimmed']
+        if trimmed:
+            singular = self._trim_whitespace(singular)
+            if plural:
+                plural = self._trim_whitespace(plural)
+
+        node = self._make_node(singular, plural, variables, plural_expr,
+                               bool(referenced),
+                               num_called_num and have_plural)
+        node.set_lineno(lineno)
+        if plural_expr_assignment is not None:
+            return [plural_expr_assignment, node]
+        else:
+            return node
+
+    def _trim_whitespace(self, string, _ws_re=re.compile(r'\s*\n\s*')):
+        return _ws_re.sub(' ', string.strip())
+
+    def _parse_block(self, parser, allow_pluralize):
+        """Parse until the next block tag with a given name."""
+        referenced = []
+        buf = []
+        while 1:
+            if parser.stream.current.type == 'data':
+                buf.append(parser.stream.current.value.replace('%', '%%'))
+                next(parser.stream)
+            elif parser.stream.current.type == 'variable_begin':
+                next(parser.stream)
+                name = parser.stream.expect('name').value
+                referenced.append(name)
+                buf.append('%%(%s)s' % name)
+                parser.stream.expect('variable_end')
+            elif parser.stream.current.type == 'block_begin':
+                next(parser.stream)
+                if parser.stream.current.test('name:endtrans'):
+                    break
+                elif parser.stream.current.test('name:pluralize'):
+                    if allow_pluralize:
+                        break
+                    parser.fail('a translatable section can have only one '
+                                'pluralize section')
+                parser.fail('control structures in translatable sections are '
+                            'not allowed')
+            elif parser.stream.eos:
+                parser.fail('unclosed translation block')
+            else:
+                assert False, 'internal parser error'
+
+        return referenced, concat(buf)
+
+    def _make_node(self, singular, plural, variables, plural_expr,
+                   vars_referenced, num_called_num):
+        """Generates a useful node from the data provided."""
+        # no variables referenced?  no need to escape for old style
+        # gettext invocations only if there are vars.
+        if not vars_referenced and not self.environment.newstyle_gettext:
+            singular = singular.replace('%%', '%')
+            if plural:
+                plural = plural.replace('%%', '%')
+
+        # singular only:
+        if plural_expr is None:
+            gettext = nodes.Name('gettext', 'load')
+            node = nodes.Call(gettext, [nodes.Const(singular)],
+                              [], None, None)
+
+        # singular and plural
+        else:
+            ngettext = nodes.Name('ngettext', 'load')
+            node = nodes.Call(ngettext, [
+                nodes.Const(singular),
+                nodes.Const(plural),
+                plural_expr
+            ], [], None, None)
+
+        # in case newstyle gettext is used, the method is powerful
+        # enough to handle the variable expansion and autoescape
+        # handling itself
+        if self.environment.newstyle_gettext:
+            for key, value in iteritems(variables):
+                # the function adds that later anyways in case num was
+                # called num, so just skip it.
+                if num_called_num and key == 'num':
+                    continue
+                node.kwargs.append(nodes.Keyword(key, value))
+
+        # otherwise do that here
+        else:
+            # mark the return value as safe if we are in an
+            # environment with autoescaping turned on
+            node = nodes.MarkSafeIfAutoescape(node)
+            if variables:
+                node = nodes.Mod(node, nodes.Dict([
+                    nodes.Pair(nodes.Const(key), value)
+                    for key, value in variables.items()
+                ]))
+        return nodes.Output([node])
+
+
+class ExprStmtExtension(Extension):
+    """Adds a `do` tag to Jinja that works like the print statement just
+    that it doesn't print the return value.
+    """
+    tags = set(['do'])
+
+    def parse(self, parser):
+        node = nodes.ExprStmt(lineno=next(parser.stream).lineno)
+        node.node = parser.parse_tuple()
+        return node
+
+
+class LoopControlExtension(Extension):
+    """Adds break and continue to the template engine."""
+    tags = set(['break', 'continue'])
+
+    def parse(self, parser):
+        token = next(parser.stream)
+        if token.value == 'break':
+            return nodes.Break(lineno=token.lineno)
+        return nodes.Continue(lineno=token.lineno)
+
+
+class WithExtension(Extension):
+    pass
+
+
+class AutoEscapeExtension(Extension):
+    pass
+
+
+class DebugExtension(Extension):
+    """A ``{% debug %}`` tag that dumps the available variables,
+    filters, and tests.
+
+    .. code-block:: html+jinja
+
+        <pre>{% debug %}</pre>
+
+    .. code-block:: text
+
+        {'context': {'cycler': <class 'jinja2.utils.Cycler'>,
+                     ...,
+                     'namespace': <class 'jinja2.utils.Namespace'>},
+         'filters': ['abs', 'attr', 'batch', 'capitalize', 'center', 'count', 'd',
+                     ..., 'urlencode', 'urlize', 'wordcount', 'wordwrap', 'xmlattr'],
+         'tests': ['!=', '<', '<=', '==', '>', '>=', 'callable', 'defined',
+                   ..., 'odd', 'sameas', 'sequence', 'string', 'undefined', 'upper']}
+
+    .. versionadded:: 2.11.0
+    """
+    tags = {'debug'}
+
+    def parse(self, parser):
+        lineno = parser.stream.expect("name:debug").lineno
+        context = ContextReference()
+        result = self.call_method("_render", [context], lineno=lineno)
+        return nodes.Output([result], lineno=lineno)
+
+    def _render(self, context):
+        result = {
+            "context": context.get_all(),
+            "filters": sorted(self.environment.filters.keys()),
+            "tests": sorted(self.environment.tests.keys()),
+        }
+
+        # Set the depth since the intent is to show the top few names.
+        if version_info[:2] >= (3, 4):
+            return pprint.pformat(result, depth=3, compact=True)
+        else:
+            return pprint.pformat(result, depth=3)
+
+
+def extract_from_ast(node, gettext_functions=GETTEXT_FUNCTIONS,
+                     babel_style=True):
+    """Extract localizable strings from the given template node.  Per
+    default this function returns matches in babel style that means non string
+    parameters as well as keyword arguments are returned as `None`.  This
+    allows Babel to figure out what you really meant if you are using
+    gettext functions that allow keyword arguments for placeholder expansion.
+    If you don't want that behavior set the `babel_style` parameter to `False`
+    which causes only strings to be returned and parameters are always stored
+    in tuples.  As a consequence invalid gettext calls (calls without a single
+    string parameter or string parameters after non-string parameters) are
+    skipped.
+
+    This example explains the behavior:
+
+    >>> from jinja2 import Environment
+    >>> env = Environment()
+    >>> node = env.parse('{{ (_("foo"), _(), ngettext("foo", "bar", 42)) }}')
+    >>> list(extract_from_ast(node))
+    [(1, '_', 'foo'), (1, '_', ()), (1, 'ngettext', ('foo', 'bar', None))]
+    >>> list(extract_from_ast(node, babel_style=False))
+    [(1, '_', ('foo',)), (1, 'ngettext', ('foo', 'bar'))]
+
+    For every string found this function yields a ``(lineno, function,
+    message)`` tuple, where:
+
+    * ``lineno`` is the number of the line on which the string was found,
+    * ``function`` is the name of the ``gettext`` function used (if the
+      string was extracted from embedded Python code), and
+    *  ``message`` is the string itself (a ``unicode`` object, or a tuple
+       of ``unicode`` objects for functions with multiple string arguments).
+
+    This extraction function operates on the AST and is because of that unable
+    to extract any comments.  For comment support you have to use the babel
+    extraction interface or extract comments yourself.
+    """
+    for node in node.find_all(nodes.Call):
+        if not isinstance(node.node, nodes.Name) or \
+           node.node.name not in gettext_functions:
+            continue
+
+        strings = []
+        for arg in node.args:
+            if isinstance(arg, nodes.Const) and \
+               isinstance(arg.value, string_types):
+                strings.append(arg.value)
+            else:
+                strings.append(None)
+
+        for arg in node.kwargs:
+            strings.append(None)
+        if node.dyn_args is not None:
+            strings.append(None)
+        if node.dyn_kwargs is not None:
+            strings.append(None)
+
+        if not babel_style:
+            strings = tuple(x for x in strings if x is not None)
+            if not strings:
+                continue
+        else:
+            if len(strings) == 1:
+                strings = strings[0]
+            else:
+                strings = tuple(strings)
+        yield node.lineno, node.node.name, strings
+
+
+class _CommentFinder(object):
+    """Helper class to find comments in a token stream.  Can only
+    find comments for gettext calls forwards.  Once the comment
+    from line 4 is found, a comment for line 1 will not return a
+    usable value.
+    """
+
+    def __init__(self, tokens, comment_tags):
+        self.tokens = tokens
+        self.comment_tags = comment_tags
+        self.offset = 0
+        self.last_lineno = 0
+
+    def find_backwards(self, offset):
+        try:
+            for _, token_type, token_value in \
+                    reversed(self.tokens[self.offset:offset]):
+                if token_type in ('comment', 'linecomment'):
+                    try:
+                        prefix, comment = token_value.split(None, 1)
+                    except ValueError:
+                        continue
+                    if prefix in self.comment_tags:
+                        return [comment.rstrip()]
+            return []
+        finally:
+            self.offset = offset
+
+    def find_comments(self, lineno):
+        if not self.comment_tags or self.last_lineno > lineno:
+            return []
+        for idx, (token_lineno, _, _) in enumerate(self.tokens[self.offset:]):
+            if token_lineno > lineno:
+                return self.find_backwards(self.offset + idx)
+        return self.find_backwards(len(self.tokens))
+
+
+def babel_extract(fileobj, keywords, comment_tags, options):
+    """Babel extraction method for Jinja templates.
+
+    .. versionchanged:: 2.3
+       Basic support for translation comments was added.  If `comment_tags`
+       is now set to a list of keywords for extraction, the extractor will
+       try to find the best preceding comment that begins with one of the
+       keywords.  For best results, make sure to not have more than one
+       gettext call in one line of code and the matching comment in the
+       same line or the line before.
+
+    .. versionchanged:: 2.5.1
+       The `newstyle_gettext` flag can be set to `True` to enable newstyle
+       gettext calls.
+
+    .. versionchanged:: 2.7
+       A `silent` option can now be provided.  If set to `False` template
+       syntax errors are propagated instead of being ignored.
+
+    :param fileobj: the file-like object the messages should be extracted from
+    :param keywords: a list of keywords (i.e. function names) that should be
+                     recognized as translation functions
+    :param comment_tags: a list of translator tags to search for and include
+                         in the results.
+    :param options: a dictionary of additional options (optional)
+    :return: an iterator over ``(lineno, funcname, message, comments)`` tuples.
+             (comments will be empty currently)
+    """
+    extensions = set()
+    for extension in options.get('extensions', '').split(','):
+        extension = extension.strip()
+        if not extension:
+            continue
+        extensions.add(import_string(extension))
+    if InternationalizationExtension not in extensions:
+        extensions.add(InternationalizationExtension)
+
+    def getbool(options, key, default=False):
+        return options.get(key, str(default)).lower() in \
+            ('1', 'on', 'yes', 'true')
+
+    silent = getbool(options, 'silent', True)
+    environment = Environment(
+        options.get('block_start_string', BLOCK_START_STRING),
+        options.get('block_end_string', BLOCK_END_STRING),
+        options.get('variable_start_string', VARIABLE_START_STRING),
+        options.get('variable_end_string', VARIABLE_END_STRING),
+        options.get('comment_start_string', COMMENT_START_STRING),
+        options.get('comment_end_string', COMMENT_END_STRING),
+        options.get('line_statement_prefix') or LINE_STATEMENT_PREFIX,
+        options.get('line_comment_prefix') or LINE_COMMENT_PREFIX,
+        getbool(options, 'trim_blocks', TRIM_BLOCKS),
+        getbool(options, 'lstrip_blocks', LSTRIP_BLOCKS),
+        NEWLINE_SEQUENCE,
+        getbool(options, 'keep_trailing_newline', KEEP_TRAILING_NEWLINE),
+        frozenset(extensions),
+        cache_size=0,
+        auto_reload=False
+    )
+
+    if getbool(options, 'trimmed'):
+        environment.policies['ext.i18n.trimmed'] = True
+    if getbool(options, 'newstyle_gettext'):
+        environment.newstyle_gettext = True
+
+    source = fileobj.read().decode(options.get('encoding', 'utf-8'))
+    try:
+        node = environment.parse(source)
+        tokens = list(environment.lex(environment.preprocess(source)))
+    except TemplateSyntaxError as e:
+        if not silent:
+            raise
+        # skip templates with syntax errors
+        return
+
+    finder = _CommentFinder(tokens, comment_tags)
+    for lineno, func, message in extract_from_ast(node, keywords):
+        yield lineno, func, message, finder.find_comments(lineno)
+
+
+#: nicer import names
+i18n = InternationalizationExtension
+do = ExprStmtExtension
+loopcontrols = LoopControlExtension
+with_ = WithExtension
+autoescape = AutoEscapeExtension
+debug = DebugExtension
diff --git a/src/jinja2/filters.py b/src/jinja2/filters.py
new file mode 100644
index 0000000..b73f627
--- /dev/null
+++ b/src/jinja2/filters.py
@@ -0,0 +1,1361 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.filters
+    ~~~~~~~~~~~~~~
+
+    Bundled jinja filters.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import re
+import math
+import random
+import warnings
+
+from itertools import groupby, chain
+from collections import namedtuple
+from jinja2.utils import Markup, escape, pformat, urlize, soft_unicode, \
+     unicode_urlencode, htmlsafe_json_dumps
+from jinja2.runtime import Undefined
+from jinja2.exceptions import FilterArgumentError
+from jinja2._compat import imap, string_types, text_type, iteritems, abc
+
+
+_word_re = re.compile(r'\w+', re.UNICODE)
+_word_beginning_split_re = re.compile(r'([-\s\(\{\[\<]+)', re.UNICODE)
+
+
+def contextfilter(f):
+    """Decorator for marking context dependent filters. The current
+    :class:`Context` will be passed as first argument.
+    """
+    f.contextfilter = True
+    return f
+
+
+def evalcontextfilter(f):
+    """Decorator for marking eval-context dependent filters.  An eval
+    context object is passed as first argument.  For more information
+    about the eval context, see :ref:`eval-context`.
+
+    .. versionadded:: 2.4
+    """
+    f.evalcontextfilter = True
+    return f
+
+
+def environmentfilter(f):
+    """Decorator for marking environment dependent filters.  The current
+    :class:`Environment` is passed to the filter as first argument.
+    """
+    f.environmentfilter = True
+    return f
+
+
+def ignore_case(value):
+    """For use as a postprocessor for :func:`make_attrgetter`. Converts strings
+    to lowercase and returns other types as-is."""
+    return value.lower() if isinstance(value, string_types) else value
+
+
+def make_attrgetter(environment, attribute, postprocess=None, default=None):
+    """Returns a callable that looks up the given attribute from a
+    passed object with the rules of the environment.  Dots are allowed
+    to access attributes of attributes.  Integer parts in paths are
+    looked up as integers.
+    """
+    attribute = _prepare_attribute_parts(attribute)
+
+    def attrgetter(item):
+        for part in attribute:
+            item = environment.getitem(item, part)
+
+            if default and isinstance(item, Undefined):
+                item = default
+
+        if postprocess is not None:
+            item = postprocess(item)
+
+        return item
+
+    return attrgetter
+
+
+def make_multi_attrgetter(environment, attribute, postprocess=None):
+    """Returns a callable that looks up the given comma separated
+    attributes from a passed object with the rules of the environment.
+    Dots are allowed to access attributes of each attribute.  Integer
+    parts in paths are looked up as integers.
+
+    The value returned by the returned callable is a list of extracted
+    attribute values.
+
+    Examples of attribute: "attr1,attr2", "attr1.inner1.0,attr2.inner2.0", etc.
+    """
+    attribute_parts = attribute.split(',') if isinstance(attribute, string_types) else [attribute]
+    attribute = [_prepare_attribute_parts(attribute_part) for attribute_part in attribute_parts]
+
+    def attrgetter(item):
+        items = [None] * len(attribute)
+        for i, attribute_part in enumerate(attribute):
+            item_i = item
+            for part in attribute_part:
+                item_i = environment.getitem(item_i, part)
+
+            if postprocess is not None:
+                item_i = postprocess(item_i)
+
+            items[i] = item_i
+        return items
+
+    return attrgetter
+
+
+def _prepare_attribute_parts(attr):
+    if attr is None:
+        return []
+    elif isinstance(attr, string_types):
+        return [int(x) if x.isdigit() else x for x in attr.split('.')]
+    else:
+        return [attr]
+
+
+def do_forceescape(value):
+    """Enforce HTML escaping.  This will probably double escape variables."""
+    if hasattr(value, '__html__'):
+        value = value.__html__()
+    return escape(text_type(value))
+
+
+def do_urlencode(value):
+    """Quote data for use in a URL path or query using UTF-8.
+
+    Basic wrapper around :func:`urllib.parse.quote` when given a
+    string, or :func:`urllib.parse.urlencode` for a dict or iterable.
+
+    :param value: Data to quote. A string will be quoted directly. A
+        dict or iterable of ``(key, value)`` pairs will be joined as a
+        query string.
+
+    When given a string, "/" is not quoted. HTTP servers treat "/" and
+    "%2F" equivalently in paths. If you need quoted slashes, use the
+    ``|replace("/", "%2F")`` filter.
+
+    .. versionadded:: 2.7
+    """
+    if isinstance(value, string_types) or not isinstance(value, abc.Iterable):
+        return unicode_urlencode(value)
+
+    if isinstance(value, dict):
+        items = iteritems(value)
+    else:
+        items = iter(value)
+
+    return u"&".join(
+        "%s=%s" % (unicode_urlencode(k, for_qs=True), unicode_urlencode(v, for_qs=True))
+        for k, v in items
+    )
+
+
+@evalcontextfilter
+def do_replace(eval_ctx, s, old, new, count=None):
+    """Return a copy of the value with all occurrences of a substring
+    replaced with a new one. The first argument is the substring
+    that should be replaced, the second is the replacement string.
+    If the optional third argument ``count`` is given, only the first
+    ``count`` occurrences are replaced:
+
+    .. sourcecode:: jinja
+
+        {{ "Hello World"|replace("Hello", "Goodbye") }}
+            -> Goodbye World
+
+        {{ "aaaaargh"|replace("a", "d'oh, ", 2) }}
+            -> d'oh, d'oh, aaargh
+    """
+    if count is None:
+        count = -1
+    if not eval_ctx.autoescape:
+        return text_type(s).replace(text_type(old), text_type(new), count)
+    if hasattr(old, '__html__') or hasattr(new, '__html__') and \
+       not hasattr(s, '__html__'):
+        s = escape(s)
+    else:
+        s = soft_unicode(s)
+    return s.replace(soft_unicode(old), soft_unicode(new), count)
+
+
+def do_upper(s):
+    """Convert a value to uppercase."""
+    return soft_unicode(s).upper()
+
+
+def do_lower(s):
+    """Convert a value to lowercase."""
+    return soft_unicode(s).lower()
+
+
+@evalcontextfilter
+def do_xmlattr(_eval_ctx, d, autospace=True):
+    """Create an SGML/XML attribute string based on the items in a dict.
+    All values that are neither `none` nor `undefined` are automatically
+    escaped:
+
+    .. sourcecode:: html+jinja
+
+        <ul{{ {'class': 'my_list', 'missing': none,
+                'id': 'list-%d'|format(variable)}|xmlattr }}>
+        ...
+        </ul>
+
+    Results in something like this:
+
+    .. sourcecode:: html
+
+        <ul class="my_list" id="list-42">
+        ...
+        </ul>
+
+    As you can see it automatically prepends a space in front of the item
+    if the filter returned something unless the second parameter is false.
+    """
+    rv = u' '.join(
+        u'%s="%s"' % (escape(key), escape(value))
+        for key, value in iteritems(d)
+        if value is not None and not isinstance(value, Undefined)
+    )
+    if autospace and rv:
+        rv = u' ' + rv
+    if _eval_ctx.autoescape:
+        rv = Markup(rv)
+    return rv
+
+
+def do_capitalize(s):
+    """Capitalize a value. The first character will be uppercase, all others
+    lowercase.
+    """
+    return soft_unicode(s).capitalize()
+
+
+def do_title(s):
+    """Return a titlecased version of the value. I.e. words will start with
+    uppercase letters, all remaining characters are lowercase.
+    """
+    return ''.join(
+        [item[0].upper() + item[1:].lower()
+         for item in _word_beginning_split_re.split(soft_unicode(s))
+         if item])
+
+
+def do_dictsort(value, case_sensitive=False, by='key', reverse=False):
+    """Sort a dict and yield (key, value) pairs. Because python dicts are
+    unsorted you may want to use this function to order them by either
+    key or value:
+
+    .. sourcecode:: jinja
+
+        {% for item in mydict|dictsort %}
+            sort the dict by key, case insensitive
+
+        {% for item in mydict|dictsort(reverse=true) %}
+            sort the dict by key, case insensitive, reverse order
+
+        {% for item in mydict|dictsort(true) %}
+            sort the dict by key, case sensitive
+
+        {% for item in mydict|dictsort(false, 'value') %}
+            sort the dict by value, case insensitive
+    """
+    if by == 'key':
+        pos = 0
+    elif by == 'value':
+        pos = 1
+    else:
+        raise FilterArgumentError(
+            'You can only sort by either "key" or "value"'
+        )
+
+    def sort_func(item):
+        value = item[pos]
+
+        if not case_sensitive:
+            value = ignore_case(value)
+
+        return value
+
+    return sorted(value.items(), key=sort_func, reverse=reverse)
+
+
+@environmentfilter
+def do_sort(environment, value, reverse=False, case_sensitive=False, attribute=None):
+    """Sort an iterable using Python's :func:`sorted`.
+
+    .. sourcecode:: jinja
+
+        {% for city in cities|sort %}
+            ...
+        {% endfor %}
+
+    :param reverse: Sort descending instead of ascending.
+    :param case_sensitive: When sorting strings, sort upper and lower
+        case separately.
+    :param attribute: When sorting objects or dicts, an attribute or
+        key to sort by. Can use dot notation like ``"address.city"``.
+        Can be a list of attributes like ``"age,name"``.
+
+    The sort is stable, it does not change the relative order of
+    elements that compare equal. This makes it is possible to chain
+    sorts on different attributes and ordering.
+
+    .. sourcecode:: jinja
+
+        {% for user in users|sort(attribute="name")|sort(reverse=true, attribute="age") %}
+            ...
+        {% endfor %}
+
+    As a shortcut to chaining when the direction is the same for all
+    attributes, pass a comma separate list of attributes.
+
+    .. sourcecode:: jinja
+
+        {% for user users|sort(attribute="age,name") %}
+            ...
+        {% endfor %}
+
+    .. versionchanged:: 2.11.0
+        The ``attribute`` parameter can be a comma separated list of
+        attributes, e.g. ``"age,name"``.
+
+    .. versionchanged:: 2.6
+       The ``attribute`` parameter was added.
+    """
+    key_func = make_multi_attrgetter(
+        environment, attribute,
+        postprocess=ignore_case if not case_sensitive else None
+    )
+    return sorted(value, key=key_func, reverse=reverse)
+
+
+@environmentfilter
+def do_unique(environment, value, case_sensitive=False, attribute=None):
+    """Returns a list of unique items from the given iterable.
+
+    .. sourcecode:: jinja
+
+        {{ ['foo', 'bar', 'foobar', 'FooBar']|unique|list }}
+            -> ['foo', 'bar', 'foobar']
+
+    The unique items are yielded in the same order as their first occurrence in
+    the iterable passed to the filter.
+
+    :param case_sensitive: Treat upper and lower case strings as distinct.
+    :param attribute: Filter objects with unique values for this attribute.
+    """
+    getter = make_attrgetter(
+        environment, attribute,
+        postprocess=ignore_case if not case_sensitive else None
+    )
+    seen = set()
+
+    for item in value:
+        key = getter(item)
+
+        if key not in seen:
+            seen.add(key)
+            yield item
+
+
+def _min_or_max(environment, value, func, case_sensitive, attribute):
+    it = iter(value)
+
+    try:
+        first = next(it)
+    except StopIteration:
+        return environment.undefined('No aggregated item, sequence was empty.')
+
+    key_func = make_attrgetter(
+        environment,
+        attribute,
+        postprocess=ignore_case if not case_sensitive else None
+    )
+    return func(chain([first], it), key=key_func)
+
+
+@environmentfilter
+def do_min(environment, value, case_sensitive=False, attribute=None):
+    """Return the smallest item from the sequence.
+
+    .. sourcecode:: jinja
+
+        {{ [1, 2, 3]|min }}
+            -> 1
+
+    :param case_sensitive: Treat upper and lower case strings as distinct.
+    :param attribute: Get the object with the min value of this attribute.
+    """
+    return _min_or_max(environment, value, min, case_sensitive, attribute)
+
+
+@environmentfilter
+def do_max(environment, value, case_sensitive=False, attribute=None):
+    """Return the largest item from the sequence.
+
+    .. sourcecode:: jinja
+
+        {{ [1, 2, 3]|max }}
+            -> 3
+
+    :param case_sensitive: Treat upper and lower case strings as distinct.
+    :param attribute: Get the object with the max value of this attribute.
+    """
+    return _min_or_max(environment, value, max, case_sensitive, attribute)
+
+
+def do_default(value, default_value=u'', boolean=False):
+    """If the value is undefined it will return the passed default value,
+    otherwise the value of the variable:
+
+    .. sourcecode:: jinja
+
+        {{ my_variable|default('my_variable is not defined') }}
+
+    This will output the value of ``my_variable`` if the variable was
+    defined, otherwise ``'my_variable is not defined'``. If you want
+    to use default with variables that evaluate to false you have to
+    set the second parameter to `true`:
+
+    .. sourcecode:: jinja
+
+        {{ ''|default('the string was empty', true) }}
+
+    .. versionchanged:: 2.11
+       It's now possible to configure the :class:`~jinja2.Environment` with
+       :class:`~jinja2.ChainableUndefined` to make the `default` filter work
+       on nested elements and attributes that may contain undefined values
+       in the chain without getting an :exc:`~jinja2.UndefinedError`.
+    """
+    if isinstance(value, Undefined) or (boolean and not value):
+        return default_value
+    return value
+
+
+@evalcontextfilter
+def do_join(eval_ctx, value, d=u'', attribute=None):
+    """Return a string which is the concatenation of the strings in the
+    sequence. The separator between elements is an empty string per
+    default, you can define it with the optional parameter:
+
+    .. sourcecode:: jinja
+
+        {{ [1, 2, 3]|join('|') }}
+            -> 1|2|3
+
+        {{ [1, 2, 3]|join }}
+            -> 123
+
+    It is also possible to join certain attributes of an object:
+
+    .. sourcecode:: jinja
+
+        {{ users|join(', ', attribute='username') }}
+
+    .. versionadded:: 2.6
+       The `attribute` parameter was added.
+    """
+    if attribute is not None:
+        value = imap(make_attrgetter(eval_ctx.environment, attribute), value)
+
+    # no automatic escaping?  joining is a lot easier then
+    if not eval_ctx.autoescape:
+        return text_type(d).join(imap(text_type, value))
+
+    # if the delimiter doesn't have an html representation we check
+    # if any of the items has.  If yes we do a coercion to Markup
+    if not hasattr(d, '__html__'):
+        value = list(value)
+        do_escape = False
+        for idx, item in enumerate(value):
+            if hasattr(item, '__html__'):
+                do_escape = True
+            else:
+                value[idx] = text_type(item)
+        if do_escape:
+            d = escape(d)
+        else:
+            d = text_type(d)
+        return d.join(value)
+
+    # no html involved, to normal joining
+    return soft_unicode(d).join(imap(soft_unicode, value))
+
+
+def do_center(value, width=80):
+    """Centers the value in a field of a given width."""
+    return text_type(value).center(width)
+
+
+@environmentfilter
+def do_first(environment, seq):
+    """Return the first item of a sequence."""
+    try:
+        return next(iter(seq))
+    except StopIteration:
+        return environment.undefined('No first item, sequence was empty.')
+
+
+@environmentfilter
+def do_last(environment, seq):
+    """
+    Return the last item of a sequence.
+
+    Note: Does not work with generators. You may want to explicitly convert it to a list:
+
+    .. sourcecode:: jinja
+
+        {{ data | selectattr('name', '==', 'Jinja') | list | last }}
+    """
+    try:
+        return next(iter(reversed(seq)))
+    except StopIteration:
+        return environment.undefined('No last item, sequence was empty.')
+
+
+@contextfilter
+def do_random(context, seq):
+    """Return a random item from the sequence."""
+    try:
+        return random.choice(seq)
+    except IndexError:
+        return context.environment.undefined('No random item, sequence was empty.')
+
+
+def do_filesizeformat(value, binary=False):
+    """Format the value like a 'human-readable' file size (i.e. 13 kB,
+    4.1 MB, 102 Bytes, etc).  Per default decimal prefixes are used (Mega,
+    Giga, etc.), if the second parameter is set to `True` the binary
+    prefixes are used (Mebi, Gibi).
+    """
+    bytes = float(value)
+    base = binary and 1024 or 1000
+    prefixes = [
+        (binary and 'KiB' or 'kB'),
+        (binary and 'MiB' or 'MB'),
+        (binary and 'GiB' or 'GB'),
+        (binary and 'TiB' or 'TB'),
+        (binary and 'PiB' or 'PB'),
+        (binary and 'EiB' or 'EB'),
+        (binary and 'ZiB' or 'ZB'),
+        (binary and 'YiB' or 'YB')
+    ]
+    if bytes == 1:
+        return '1 Byte'
+    elif bytes < base:
+        return '%d Bytes' % bytes
+    else:
+        for i, prefix in enumerate(prefixes):
+            unit = base ** (i + 2)
+            if bytes < unit:
+                return '%.1f %s' % ((base * bytes / unit), prefix)
+        return '%.1f %s' % ((base * bytes / unit), prefix)
+
+
+def do_pprint(value, verbose=False):
+    """Pretty print a variable. Useful for debugging.
+
+    With Jinja 1.2 onwards you can pass it a parameter.  If this parameter
+    is truthy the output will be more verbose (this requires `pretty`)
+    """
+    return pformat(value, verbose=verbose)
+
+
+@evalcontextfilter
+def do_urlize(eval_ctx, value, trim_url_limit=None, nofollow=False,
+              target=None, rel=None):
+    """Converts URLs in plain text into clickable links.
+
+    If you pass the filter an additional integer it will shorten the urls
+    to that number. Also a third argument exists that makes the urls
+    "nofollow":
+
+    .. sourcecode:: jinja
+
+        {{ mytext|urlize(40, true) }}
+            links are shortened to 40 chars and defined with rel="nofollow"
+
+    If *target* is specified, the ``target`` attribute will be added to the
+    ``<a>`` tag:
+
+    .. sourcecode:: jinja
+
+       {{ mytext|urlize(40, target='_blank') }}
+
+    .. versionchanged:: 2.8+
+       The *target* parameter was added.
+    """
+    policies = eval_ctx.environment.policies
+    rel = set((rel or '').split() or [])
+    if nofollow:
+        rel.add('nofollow')
+    rel.update((policies['urlize.rel'] or '').split())
+    if target is None:
+        target = policies['urlize.target']
+    rel = ' '.join(sorted(rel)) or None
+    rv = urlize(value, trim_url_limit, rel=rel, target=target)
+    if eval_ctx.autoescape:
+        rv = Markup(rv)
+    return rv
+
+
+def do_indent(
+    s, width=4, first=False, blank=False, indentfirst=None
+):
+    """Return a copy of the string with each line indented by 4 spaces. The
+    first line and blank lines are not indented by default.
+
+    :param width: Number of spaces to indent by.
+    :param first: Don't skip indenting the first line.
+    :param blank: Don't skip indenting empty lines.
+
+    .. versionchanged:: 2.10
+        Blank lines are not indented by default.
+
+        Rename the ``indentfirst`` argument to ``first``.
+    """
+    if indentfirst is not None:
+        warnings.warn(DeprecationWarning(
+            'The "indentfirst" argument is renamed to "first".'
+        ), stacklevel=2)
+        first = indentfirst
+
+    indention = u' ' * width
+    newline = u'\n'
+
+    if isinstance(s, Markup):
+        indention = Markup(indention)
+        newline = Markup(newline)
+
+    s += newline  # this quirk is necessary for splitlines method
+
+    if blank:
+        rv = (newline + indention).join(s.splitlines())
+    else:
+        lines = s.splitlines()
+        rv = lines.pop(0)
+
+        if lines:
+            rv += newline + newline.join(
+                indention + line if line else line for line in lines
+            )
+
+    if first:
+        rv = indention + rv
+
+    return rv
+
+
+@environmentfilter
+def do_truncate(env, s, length=255, killwords=False, end='...', leeway=None):
+    """Return a truncated copy of the string. The length is specified
+    with the first parameter which defaults to ``255``. If the second
+    parameter is ``true`` the filter will cut the text at length. Otherwise
+    it will discard the last word. If the text was in fact
+    truncated it will append an ellipsis sign (``"..."``). If you want a
+    different ellipsis sign than ``"..."`` you can specify it using the
+    third parameter. Strings that only exceed the length by the tolerance
+    margin given in the fourth parameter will not be truncated.
+
+    .. sourcecode:: jinja
+
+        {{ "foo bar baz qux"|truncate(9) }}
+            -> "foo..."
+        {{ "foo bar baz qux"|truncate(9, True) }}
+            -> "foo ba..."
+        {{ "foo bar baz qux"|truncate(11) }}
+            -> "foo bar baz qux"
+        {{ "foo bar baz qux"|truncate(11, False, '...', 0) }}
+            -> "foo bar..."
+
+    The default leeway on newer Jinja versions is 5 and was 0 before but
+    can be reconfigured globally.
+    """
+    if leeway is None:
+        leeway = env.policies['truncate.leeway']
+    assert length >= len(end), 'expected length >= %s, got %s' % (len(end), length)
+    assert leeway >= 0, 'expected leeway >= 0, got %s' % leeway
+    if len(s) <= length + leeway:
+        return s
+    if killwords:
+        return s[:length - len(end)] + end
+    result = s[:length - len(end)].rsplit(' ', 1)[0]
+    return result + end
+
+
+@environmentfilter
+def do_wordwrap(
+    environment,
+    s,
+    width=79,
+    break_long_words=True,
+    wrapstring=None,
+    break_on_hyphens=True,
+):
+    """Wrap a string to the given width. Existing newlines are treated
+    as paragraphs to be wrapped separately.
+
+    :param s: Original text to wrap.
+    :param width: Maximum length of wrapped lines.
+    :param break_long_words: If a word is longer than ``width``, break
+        it across lines.
+    :param break_on_hyphens: If a word contains hyphens, it may be split
+        across lines.
+    :param wrapstring: String to join each wrapped line. Defaults to
+        :attr:`Environment.newline_sequence`.
+
+    .. versionchanged:: 2.11
+        Existing newlines are treated as paragraphs wrapped separately.
+
+    .. versionchanged:: 2.11
+        Added the ``break_on_hyphens`` parameter.
+
+    .. versionchanged:: 2.7
+        Added the ``wrapstring`` parameter.
+    """
+
+    import textwrap
+
+    if not wrapstring:
+        wrapstring = environment.newline_sequence
+
+    # textwrap.wrap doesn't consider existing newlines when wrapping.
+    # If the string has a newline before width, wrap will still insert
+    # a newline at width, resulting in a short line. Instead, split and
+    # wrap each paragraph individually.
+    return wrapstring.join(
+        [
+            wrapstring.join(
+                textwrap.wrap(
+                    line,
+                    width=width,
+                    expand_tabs=False,
+                    replace_whitespace=False,
+                    break_long_words=break_long_words,
+                    break_on_hyphens=break_on_hyphens,
+                )
+            )
+            for line in s.splitlines()
+        ]
+    )
+
+
+def do_wordcount(s):
+    """Count the words in that string."""
+    return len(_word_re.findall(s))
+
+
+def do_int(value, default=0, base=10):
+    """Convert the value into an integer. If the
+    conversion doesn't work it will return ``0``. You can
+    override this default using the first parameter. You
+    can also override the default base (10) in the second
+    parameter, which handles input with prefixes such as
+    0b, 0o and 0x for bases 2, 8 and 16 respectively.
+    The base is ignored for decimal numbers and non-string values.
+    """
+    try:
+        if isinstance(value, string_types):
+            return int(value, base)
+        return int(value)
+    except (TypeError, ValueError):
+        # this quirk is necessary so that "42.23"|int gives 42.
+        try:
+            return int(float(value))
+        except (TypeError, ValueError):
+            return default
+
+
+def do_float(value, default=0.0):
+    """Convert the value into a floating point number. If the
+    conversion doesn't work it will return ``0.0``. You can
+    override this default using the first parameter.
+    """
+    try:
+        return float(value)
+    except (TypeError, ValueError):
+        return default
+
+
+def do_format(value, *args, **kwargs):
+    """Apply the given values to a `printf-style`_ format string, like
+    ``string % values``.
+
+    .. sourcecode:: jinja
+
+        {{ "%s, %s!"|format(greeting, name) }}
+        Hello, World!
+
+    In most cases it should be more convenient and efficient to use the
+    ``%`` operator or :meth:`str.format`.
+
+    .. code-block:: text
+
+        {{ "%s, %s!" % (greeting, name) }}
+        {{ "{}, {}!".format(greeting, name) }}
+
+    .. _printf-style: https://docs.python.org/library/stdtypes.html
+        #printf-style-string-formatting
+    """
+    if args and kwargs:
+        raise FilterArgumentError('can\'t handle positional and keyword '
+                                  'arguments at the same time')
+    return soft_unicode(value) % (kwargs or args)
+
+
+def do_trim(value, chars=None):
+    """Strip leading and trailing characters, by default whitespace."""
+    return soft_unicode(value).strip(chars)
+
+
+def do_striptags(value):
+    """Strip SGML/XML tags and replace adjacent whitespace by one space.
+    """
+    if hasattr(value, '__html__'):
+        value = value.__html__()
+    return Markup(text_type(value)).striptags()
+
+
+def do_slice(value, slices, fill_with=None):
+    """Slice an iterator and return a list of lists containing
+    those items. Useful if you want to create a div containing
+    three ul tags that represent columns:
+
+    .. sourcecode:: html+jinja
+
+        <div class="columnwrapper">
+          {%- for column in items|slice(3) %}
+            <ul class="column-{{ loop.index }}">
+            {%- for item in column %}
+              <li>{{ item }}</li>
+            {%- endfor %}
+            </ul>
+          {%- endfor %}
+        </div>
+
+    If you pass it a second argument it's used to fill missing
+    values on the last iteration.
+    """
+    seq = list(value)
+    length = len(seq)
+    items_per_slice = length // slices
+    slices_with_extra = length % slices
+    offset = 0
+    for slice_number in range(slices):
+        start = offset + slice_number * items_per_slice
+        if slice_number < slices_with_extra:
+            offset += 1
+        end = offset + (slice_number + 1) * items_per_slice
+        tmp = seq[start:end]
+        if fill_with is not None and slice_number >= slices_with_extra:
+            tmp.append(fill_with)
+        yield tmp
+
+
+def do_batch(value, linecount, fill_with=None):
+    """
+    A filter that batches items. It works pretty much like `slice`
+    just the other way round. It returns a list of lists with the
+    given number of items. If you provide a second parameter this
+    is used to fill up missing items. See this example:
+
+    .. sourcecode:: html+jinja
+
+        <table>
+        {%- for row in items|batch(3, '&nbsp;') %}
+          <tr>
+          {%- for column in row %}
+            <td>{{ column }}</td>
+          {%- endfor %}
+          </tr>
+        {%- endfor %}
+        </table>
+    """
+    tmp = []
+    for item in value:
+        if len(tmp) == linecount:
+            yield tmp
+            tmp = []
+        tmp.append(item)
+    if tmp:
+        if fill_with is not None and len(tmp) < linecount:
+            tmp += [fill_with] * (linecount - len(tmp))
+        yield tmp
+
+
+def do_round(value, precision=0, method='common'):
+    """Round the number to a given precision. The first
+    parameter specifies the precision (default is ``0``), the
+    second the rounding method:
+
+    - ``'common'`` rounds either up or down
+    - ``'ceil'`` always rounds up
+    - ``'floor'`` always rounds down
+
+    If you don't specify a method ``'common'`` is used.
+
+    .. sourcecode:: jinja
+
+        {{ 42.55|round }}
+            -> 43.0
+        {{ 42.55|round(1, 'floor') }}
+            -> 42.5
+
+    Note that even if rounded to 0 precision, a float is returned.  If
+    you need a real integer, pipe it through `int`:
+
+    .. sourcecode:: jinja
+
+        {{ 42.55|round|int }}
+            -> 43
+    """
+    if not method in ('common', 'ceil', 'floor'):
+        raise FilterArgumentError('method must be common, ceil or floor')
+    if method == 'common':
+        return round(value, precision)
+    func = getattr(math, method)
+    return func(value * (10 ** precision)) / (10 ** precision)
+
+
+# Use a regular tuple repr here.  This is what we did in the past and we
+# really want to hide this custom type as much as possible.  In particular
+# we do not want to accidentally expose an auto generated repr in case
+# people start to print this out in comments or something similar for
+# debugging.
+_GroupTuple = namedtuple('_GroupTuple', ['grouper', 'list'])
+_GroupTuple.__repr__ = tuple.__repr__
+_GroupTuple.__str__ = tuple.__str__
+
+
+@environmentfilter
+def do_groupby(environment, value, attribute):
+    """Group a sequence of objects by an attribute using Python's
+    :func:`itertools.groupby`. The attribute can use dot notation for
+    nested access, like ``"address.city"``. Unlike Python's ``groupby``,
+    the values are sorted first so only one group is returned for each
+    unique value.
+
+    For example, a list of ``User`` objects with a ``city`` attribute
+    can be rendered in groups. In this example, ``grouper`` refers to
+    the ``city`` value of the group.
+
+    .. sourcecode:: html+jinja
+
+        <ul>{% for city, items in users|groupby("city") %}
+          <li>{{ city }}
+            <ul>{% for user in items %}
+              <li>{{ user.name }}
+            {% endfor %}</ul>
+          </li>
+        {% endfor %}</ul>
+
+    ``groupby`` yields namedtuples of ``(grouper, list)``, which
+    can be used instead of the tuple unpacking above. ``grouper`` is the
+    value of the attribute, and ``list`` is the items with that value.
+
+    .. sourcecode:: html+jinja
+
+        <ul>{% for group in users|groupby("city") %}
+          <li>{{ group.grouper }}: {{ group.list|join(", ") }}
+        {% endfor %}</ul>
+
+    .. versionchanged:: 2.6
+        The attribute supports dot notation for nested access.
+    """
+    expr = make_attrgetter(environment, attribute)
+    return [_GroupTuple(key, list(values)) for key, values
+            in groupby(sorted(value, key=expr), expr)]
+
+
+@environmentfilter
+def do_sum(environment, iterable, attribute=None, start=0):
+    """Returns the sum of a sequence of numbers plus the value of parameter
+    'start' (which defaults to 0).  When the sequence is empty it returns
+    start.
+
+    It is also possible to sum up only certain attributes:
+
+    .. sourcecode:: jinja
+
+        Total: {{ items|sum(attribute='price') }}
+
+    .. versionchanged:: 2.6
+       The `attribute` parameter was added to allow suming up over
+       attributes.  Also the `start` parameter was moved on to the right.
+    """
+    if attribute is not None:
+        iterable = imap(make_attrgetter(environment, attribute), iterable)
+    return sum(iterable, start)
+
+
+def do_list(value):
+    """Convert the value into a list.  If it was a string the returned list
+    will be a list of characters.
+    """
+    return list(value)
+
+
+def do_mark_safe(value):
+    """Mark the value as safe which means that in an environment with automatic
+    escaping enabled this variable will not be escaped.
+    """
+    return Markup(value)
+
+
+def do_mark_unsafe(value):
+    """Mark a value as unsafe.  This is the reverse operation for :func:`safe`."""
+    return text_type(value)
+
+
+def do_reverse(value):
+    """Reverse the object or return an iterator that iterates over it the other
+    way round.
+    """
+    if isinstance(value, string_types):
+        return value[::-1]
+    try:
+        return reversed(value)
+    except TypeError:
+        try:
+            rv = list(value)
+            rv.reverse()
+            return rv
+        except TypeError:
+            raise FilterArgumentError('argument must be iterable')
+
+
+@environmentfilter
+def do_attr(environment, obj, name):
+    """Get an attribute of an object.  ``foo|attr("bar")`` works like
+    ``foo.bar`` just that always an attribute is returned and items are not
+    looked up.
+
+    See :ref:`Notes on subscriptions <notes-on-subscriptions>` for more details.
+    """
+    try:
+        name = str(name)
+    except UnicodeError:
+        pass
+    else:
+        try:
+            value = getattr(obj, name)
+        except AttributeError:
+            pass
+        else:
+            if environment.sandboxed and not \
+               environment.is_safe_attribute(obj, name, value):
+                return environment.unsafe_undefined(obj, name)
+            return value
+    return environment.undefined(obj=obj, name=name)
+
+
+@contextfilter
+def do_map(*args, **kwargs):
+    """Applies a filter on a sequence of objects or looks up an attribute.
+    This is useful when dealing with lists of objects but you are really
+    only interested in a certain value of it.
+
+    The basic usage is mapping on an attribute.  Imagine you have a list
+    of users but you are only interested in a list of usernames:
+
+    .. sourcecode:: jinja
+
+        Users on this page: {{ users|map(attribute='username')|join(', ') }}
+
+    You can specify a ``default`` value to use if an object in the list
+    does not have the given attribute.
+
+    .. sourcecode:: jinja
+
+        {{ users|map(attribute="username", default="Anonymous")|join(", ") }}
+
+    Alternatively you can let it invoke a filter by passing the name of the
+    filter and the arguments afterwards.  A good example would be applying a
+    text conversion filter on a sequence:
+
+    .. sourcecode:: jinja
+
+        Users on this page: {{ titles|map('lower')|join(', ') }}
+
+    Similar to a generator comprehension such as:
+
+    .. code-block:: python
+
+        (u.username for u in users)
+        (u.username or "Anonymous" for u in users)
+        (do_lower(x) for x in titles)
+
+    .. versionchanged:: 2.11.0
+        Added the ``default`` parameter.
+
+    .. versionadded:: 2.7
+    """
+    seq, func = prepare_map(args, kwargs)
+    if seq:
+        for item in seq:
+            yield func(item)
+
+
+@contextfilter
+def do_select(*args, **kwargs):
+    """Filters a sequence of objects by applying a test to each object,
+    and only selecting the objects with the test succeeding.
+
+    If no test is specified, each object will be evaluated as a boolean.
+
+    Example usage:
+
+    .. sourcecode:: jinja
+
+        {{ numbers|select("odd") }}
+        {{ numbers|select("odd") }}
+        {{ numbers|select("divisibleby", 3) }}
+        {{ numbers|select("lessthan", 42) }}
+        {{ strings|select("equalto", "mystring") }}
+
+    Similar to a generator comprehension such as:
+
+    .. code-block:: python
+
+        (n for n in numbers if test_odd(n))
+        (n for n in numbers if test_divisibleby(n, 3))
+
+    .. versionadded:: 2.7
+    """
+    return select_or_reject(args, kwargs, lambda x: x, False)
+
+
+@contextfilter
+def do_reject(*args, **kwargs):
+    """Filters a sequence of objects by applying a test to each object,
+    and rejecting the objects with the test succeeding.
+
+    If no test is specified, each object will be evaluated as a boolean.
+
+    Example usage:
+
+    .. sourcecode:: jinja
+
+        {{ numbers|reject("odd") }}
+
+    Similar to a generator comprehension such as:
+
+    .. code-block:: python
+
+        (n for n in numbers if not test_odd(n))
+
+    .. versionadded:: 2.7
+    """
+    return select_or_reject(args, kwargs, lambda x: not x, False)
+
+
+@contextfilter
+def do_selectattr(*args, **kwargs):
+    """Filters a sequence of objects by applying a test to the specified
+    attribute of each object, and only selecting the objects with the
+    test succeeding.
+
+    If no test is specified, the attribute's value will be evaluated as
+    a boolean.
+
+    Example usage:
+
+    .. sourcecode:: jinja
+
+        {{ users|selectattr("is_active") }}
+        {{ users|selectattr("email", "none") }}
+
+    Similar to a generator comprehension such as:
+
+    .. code-block:: python
+
+        (u for user in users if user.is_active)
+        (u for user in users if test_none(user.email))
+
+    .. versionadded:: 2.7
+    """
+    return select_or_reject(args, kwargs, lambda x: x, True)
+
+
+@contextfilter
+def do_rejectattr(*args, **kwargs):
+    """Filters a sequence of objects by applying a test to the specified
+    attribute of each object, and rejecting the objects with the test
+    succeeding.
+
+    If no test is specified, the attribute's value will be evaluated as
+    a boolean.
+
+    .. sourcecode:: jinja
+
+        {{ users|rejectattr("is_active") }}
+        {{ users|rejectattr("email", "none") }}
+
+    Similar to a generator comprehension such as:
+
+    .. code-block:: python
+
+        (u for user in users if not user.is_active)
+        (u for user in users if not test_none(user.email))
+
+    .. versionadded:: 2.7
+    """
+    return select_or_reject(args, kwargs, lambda x: not x, True)
+
+
+@evalcontextfilter
+def do_tojson(eval_ctx, value, indent=None):
+    """Dumps a structure to JSON so that it's safe to use in ``<script>``
+    tags.  It accepts the same arguments and returns a JSON string.  Note that
+    this is available in templates through the ``|tojson`` filter which will
+    also mark the result as safe.  Due to how this function escapes certain
+    characters this is safe even if used outside of ``<script>`` tags.
+
+    The following characters are escaped in strings:
+
+    -   ``<``
+    -   ``>``
+    -   ``&``
+    -   ``'``
+
+    This makes it safe to embed such strings in any place in HTML with the
+    notable exception of double quoted attributes.  In that case single
+    quote your attributes or HTML escape it in addition.
+
+    The indent parameter can be used to enable pretty printing.  Set it to
+    the number of spaces that the structures should be indented with.
+
+    Note that this filter is for use in HTML contexts only.
+
+    .. versionadded:: 2.9
+    """
+    policies = eval_ctx.environment.policies
+    dumper = policies['json.dumps_function']
+    options = policies['json.dumps_kwargs']
+    if indent is not None:
+        options = dict(options)
+        options['indent'] = indent
+    return htmlsafe_json_dumps(value, dumper=dumper, **options)
+
+
+def prepare_map(args, kwargs):
+    context = args[0]
+    seq = args[1]
+    default = None
+
+    if len(args) == 2 and 'attribute' in kwargs:
+        attribute = kwargs.pop('attribute')
+        default = kwargs.pop('default', None)
+        if kwargs:
+            raise FilterArgumentError('Unexpected keyword argument %r' %
+                next(iter(kwargs)))
+        func = make_attrgetter(context.environment, attribute, default=default)
+    else:
+        try:
+            name = args[2]
+            args = args[3:]
+        except LookupError:
+            raise FilterArgumentError('map requires a filter argument')
+        func = lambda item: context.environment.call_filter(
+            name, item, args, kwargs, context=context)
+
+    return seq, func
+
+
+def prepare_select_or_reject(args, kwargs, modfunc, lookup_attr):
+    context = args[0]
+    seq = args[1]
+    if lookup_attr:
+        try:
+            attr = args[2]
+        except LookupError:
+            raise FilterArgumentError('Missing parameter for attribute name')
+        transfunc = make_attrgetter(context.environment, attr)
+        off = 1
+    else:
+        off = 0
+        transfunc = lambda x: x
+
+    try:
+        name = args[2 + off]
+        args = args[3 + off:]
+        func = lambda item: context.environment.call_test(
+            name, item, args, kwargs)
+    except LookupError:
+        func = bool
+
+    return seq, lambda item: modfunc(func(transfunc(item)))
+
+
+def select_or_reject(args, kwargs, modfunc, lookup_attr):
+    seq, func = prepare_select_or_reject(args, kwargs, modfunc, lookup_attr)
+    if seq:
+        for item in seq:
+            if func(item):
+                yield item
+
+
+FILTERS = {
+    'abs':                  abs,
+    'attr':                 do_attr,
+    'batch':                do_batch,
+    'capitalize':           do_capitalize,
+    'center':               do_center,
+    'count':                len,
+    'd':                    do_default,
+    'default':              do_default,
+    'dictsort':             do_dictsort,
+    'e':                    escape,
+    'escape':               escape,
+    'filesizeformat':       do_filesizeformat,
+    'first':                do_first,
+    'float':                do_float,
+    'forceescape':          do_forceescape,
+    'format':               do_format,
+    'groupby':              do_groupby,
+    'indent':               do_indent,
+    'int':                  do_int,
+    'join':                 do_join,
+    'last':                 do_last,
+    'length':               len,
+    'list':                 do_list,
+    'lower':                do_lower,
+    'map':                  do_map,
+    'min':                  do_min,
+    'max':                  do_max,
+    'pprint':               do_pprint,
+    'random':               do_random,
+    'reject':               do_reject,
+    'rejectattr':           do_rejectattr,
+    'replace':              do_replace,
+    'reverse':              do_reverse,
+    'round':                do_round,
+    'safe':                 do_mark_safe,
+    'select':               do_select,
+    'selectattr':           do_selectattr,
+    'slice':                do_slice,
+    'sort':                 do_sort,
+    'string':               soft_unicode,
+    'striptags':            do_striptags,
+    'sum':                  do_sum,
+    'title':                do_title,
+    'trim':                 do_trim,
+    'truncate':             do_truncate,
+    'unique':               do_unique,
+    'upper':                do_upper,
+    'urlencode':            do_urlencode,
+    'urlize':               do_urlize,
+    'wordcount':            do_wordcount,
+    'wordwrap':             do_wordwrap,
+    'xmlattr':              do_xmlattr,
+    'tojson':               do_tojson,
+}
diff --git a/src/jinja2/idtracking.py b/src/jinja2/idtracking.py
new file mode 100644
index 0000000..491bfe0
--- /dev/null
+++ b/src/jinja2/idtracking.py
@@ -0,0 +1,286 @@
+from jinja2.visitor import NodeVisitor
+from jinja2._compat import iteritems
+
+
+VAR_LOAD_PARAMETER = 'param'
+VAR_LOAD_RESOLVE = 'resolve'
+VAR_LOAD_ALIAS = 'alias'
+VAR_LOAD_UNDEFINED = 'undefined'
+
+
+def find_symbols(nodes, parent_symbols=None):
+    sym = Symbols(parent=parent_symbols)
+    visitor = FrameSymbolVisitor(sym)
+    for node in nodes:
+        visitor.visit(node)
+    return sym
+
+
+def symbols_for_node(node, parent_symbols=None):
+    sym = Symbols(parent=parent_symbols)
+    sym.analyze_node(node)
+    return sym
+
+
+class Symbols(object):
+
+    def __init__(self, parent=None, level=None):
+        if level is None:
+            if parent is None:
+                level = 0
+            else:
+                level = parent.level + 1
+        self.level = level
+        self.parent = parent
+        self.refs = {}
+        self.loads = {}
+        self.stores = set()
+
+    def analyze_node(self, node, **kwargs):
+        visitor = RootVisitor(self)
+        visitor.visit(node, **kwargs)
+
+    def _define_ref(self, name, load=None):
+        ident = 'l_%d_%s' % (self.level, name)
+        self.refs[name] = ident
+        if load is not None:
+            self.loads[ident] = load
+        return ident
+
+    def find_load(self, target):
+        if target in self.loads:
+            return self.loads[target]
+        if self.parent is not None:
+            return self.parent.find_load(target)
+
+    def find_ref(self, name):
+        if name in self.refs:
+            return self.refs[name]
+        if self.parent is not None:
+            return self.parent.find_ref(name)
+
+    def ref(self, name):
+        rv = self.find_ref(name)
+        if rv is None:
+            raise AssertionError('Tried to resolve a name to a reference that '
+                                 'was unknown to the frame (%r)' % name)
+        return rv
+
+    def copy(self):
+        rv = object.__new__(self.__class__)
+        rv.__dict__.update(self.__dict__)
+        rv.refs = self.refs.copy()
+        rv.loads = self.loads.copy()
+        rv.stores = self.stores.copy()
+        return rv
+
+    def store(self, name):
+        self.stores.add(name)
+
+        # If we have not see the name referenced yet, we need to figure
+        # out what to set it to.
+        if name not in self.refs:
+            # If there is a parent scope we check if the name has a
+            # reference there.  If it does it means we might have to alias
+            # to a variable there.
+            if self.parent is not None:
+                outer_ref = self.parent.find_ref(name)
+                if outer_ref is not None:
+                    self._define_ref(name, load=(VAR_LOAD_ALIAS, outer_ref))
+                    return
+
+            # Otherwise we can just set it to undefined.
+            self._define_ref(name, load=(VAR_LOAD_UNDEFINED, None))
+
+    def declare_parameter(self, name):
+        self.stores.add(name)
+        return self._define_ref(name, load=(VAR_LOAD_PARAMETER, None))
+
+    def load(self, name):
+        target = self.find_ref(name)
+        if target is None:
+            self._define_ref(name, load=(VAR_LOAD_RESOLVE, name))
+
+    def branch_update(self, branch_symbols):
+        stores = {}
+        for branch in branch_symbols:
+            for target in branch.stores:
+                if target in self.stores:
+                    continue
+                stores[target] = stores.get(target, 0) + 1
+
+        for sym in branch_symbols:
+            self.refs.update(sym.refs)
+            self.loads.update(sym.loads)
+            self.stores.update(sym.stores)
+
+        for name, branch_count in iteritems(stores):
+            if branch_count == len(branch_symbols):
+                continue
+            target = self.find_ref(name)
+            assert target is not None, 'should not happen'
+
+            if self.parent is not None:
+                outer_target = self.parent.find_ref(name)
+                if outer_target is not None:
+                    self.loads[target] = (VAR_LOAD_ALIAS, outer_target)
+                    continue
+            self.loads[target] = (VAR_LOAD_RESOLVE, name)
+
+    def dump_stores(self):
+        rv = {}
+        node = self
+        while node is not None:
+            for name in node.stores:
+                if name not in rv:
+                    rv[name] = self.find_ref(name)
+            node = node.parent
+        return rv
+
+    def dump_param_targets(self):
+        rv = set()
+        node = self
+        while node is not None:
+            for target, (instr, _) in iteritems(self.loads):
+                if instr == VAR_LOAD_PARAMETER:
+                    rv.add(target)
+            node = node.parent
+        return rv
+
+
+class RootVisitor(NodeVisitor):
+
+    def __init__(self, symbols):
+        self.sym_visitor = FrameSymbolVisitor(symbols)
+
+    def _simple_visit(self, node, **kwargs):
+        for child in node.iter_child_nodes():
+            self.sym_visitor.visit(child)
+
+    visit_Template = visit_Block = visit_Macro = visit_FilterBlock = \
+        visit_Scope = visit_If = visit_ScopedEvalContextModifier = \
+        _simple_visit
+
+    def visit_AssignBlock(self, node, **kwargs):
+        for child in node.body:
+            self.sym_visitor.visit(child)
+
+    def visit_CallBlock(self, node, **kwargs):
+        for child in node.iter_child_nodes(exclude=('call',)):
+            self.sym_visitor.visit(child)
+
+    def visit_OverlayScope(self, node, **kwargs):
+        for child in node.body:
+            self.sym_visitor.visit(child)
+
+    def visit_For(self, node, for_branch='body', **kwargs):
+        if for_branch == 'body':
+            self.sym_visitor.visit(node.target, store_as_param=True)
+            branch = node.body
+        elif for_branch == 'else':
+            branch = node.else_
+        elif for_branch == 'test':
+            self.sym_visitor.visit(node.target, store_as_param=True)
+            if node.test is not None:
+                self.sym_visitor.visit(node.test)
+            return
+        else:
+            raise RuntimeError('Unknown for branch')
+        for item in branch or ():
+            self.sym_visitor.visit(item)
+
+    def visit_With(self, node, **kwargs):
+        for target in node.targets:
+            self.sym_visitor.visit(target)
+        for child in node.body:
+            self.sym_visitor.visit(child)
+
+    def generic_visit(self, node, *args, **kwargs):
+        raise NotImplementedError('Cannot find symbols for %r' %
+                                  node.__class__.__name__)
+
+
+class FrameSymbolVisitor(NodeVisitor):
+    """A visitor for `Frame.inspect`."""
+
+    def __init__(self, symbols):
+        self.symbols = symbols
+
+    def visit_Name(self, node, store_as_param=False, **kwargs):
+        """All assignments to names go through this function."""
+        if store_as_param or node.ctx == 'param':
+            self.symbols.declare_parameter(node.name)
+        elif node.ctx == 'store':
+            self.symbols.store(node.name)
+        elif node.ctx == 'load':
+            self.symbols.load(node.name)
+
+    def visit_NSRef(self, node, **kwargs):
+        self.symbols.load(node.name)
+
+    def visit_If(self, node, **kwargs):
+        self.visit(node.test, **kwargs)
+
+        original_symbols = self.symbols
+
+        def inner_visit(nodes):
+            self.symbols = rv = original_symbols.copy()
+            for subnode in nodes:
+                self.visit(subnode, **kwargs)
+            self.symbols = original_symbols
+            return rv
+
+        body_symbols = inner_visit(node.body)
+        elif_symbols = inner_visit(node.elif_)
+        else_symbols = inner_visit(node.else_ or ())
+
+        self.symbols.branch_update([body_symbols, elif_symbols, else_symbols])
+
+    def visit_Macro(self, node, **kwargs):
+        self.symbols.store(node.name)
+
+    def visit_Import(self, node, **kwargs):
+        self.generic_visit(node, **kwargs)
+        self.symbols.store(node.target)
+
+    def visit_FromImport(self, node, **kwargs):
+        self.generic_visit(node, **kwargs)
+        for name in node.names:
+            if isinstance(name, tuple):
+                self.symbols.store(name[1])
+            else:
+                self.symbols.store(name)
+
+    def visit_Assign(self, node, **kwargs):
+        """Visit assignments in the correct order."""
+        self.visit(node.node, **kwargs)
+        self.visit(node.target, **kwargs)
+
+    def visit_For(self, node, **kwargs):
+        """Visiting stops at for blocks.  However the block sequence
+        is visited as part of the outer scope.
+        """
+        self.visit(node.iter, **kwargs)
+
+    def visit_CallBlock(self, node, **kwargs):
+        self.visit(node.call, **kwargs)
+
+    def visit_FilterBlock(self, node, **kwargs):
+        self.visit(node.filter, **kwargs)
+
+    def visit_With(self, node, **kwargs):
+        for target in node.values:
+            self.visit(target)
+
+    def visit_AssignBlock(self, node, **kwargs):
+        """Stop visiting at block assigns."""
+        self.visit(node.target, **kwargs)
+
+    def visit_Scope(self, node, **kwargs):
+        """Stop visiting at scopes."""
+
+    def visit_Block(self, node, **kwargs):
+        """Stop visiting at blocks."""
+
+    def visit_OverlayScope(self, node, **kwargs):
+        """Do not visit into overlay scopes."""
diff --git a/src/jinja2/lexer.py b/src/jinja2/lexer.py
new file mode 100644
index 0000000..910a931
--- /dev/null
+++ b/src/jinja2/lexer.py
@@ -0,0 +1,766 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.lexer
+    ~~~~~~~~~~~~
+
+    This module implements a Jinja / Python combination lexer. The
+    `Lexer` class provided by this module is used to do some preprocessing
+    for Jinja.
+
+    On the one hand it filters out invalid operators like the bitshift
+    operators we don't allow in templates. On the other hand it separates
+    template code and python code in expressions.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import re
+from ast import literal_eval
+from collections import deque
+from operator import itemgetter
+
+from jinja2._compat import implements_iterator, intern, iteritems, text_type
+from jinja2.exceptions import TemplateSyntaxError
+from jinja2.utils import LRUCache
+
+# cache for the lexers. Exists in order to be able to have multiple
+# environments with the same lexer
+_lexer_cache = LRUCache(50)
+
+# static regular expressions
+whitespace_re = re.compile(r'\s+', re.U)
+newline_re = re.compile(r'(\r\n|\r|\n)')
+string_re = re.compile(r"('([^'\\]*(?:\\.[^'\\]*)*)'"
+                       r'|"([^"\\]*(?:\\.[^"\\]*)*)")', re.S)
+integer_re = re.compile(r'(\d+_)*\d+')
+float_re = re.compile(
+    r"""
+    (?<!\.)  # doesn't start with a .
+    (\d+_)*\d+  # digits, possibly _ separated
+    (
+        (\.(\d+_)*\d+)?  # optional fractional part
+        e[+\-]?(\d+_)*\d+  # exponent part
+    |
+        \.(\d+_)*\d+  # required fractional part
+    )
+    """,
+    re.IGNORECASE | re.VERBOSE,
+)
+
+try:
+    # check if this Python supports Unicode identifiers
+    compile('föö', '<unknown>', 'eval')
+except SyntaxError:
+    # no Unicode support, use ASCII identifiers
+    name_re = re.compile(r'[a-zA-Z_][a-zA-Z0-9_]*')
+    check_ident = False
+else:
+    # Unicode support, build a pattern to match valid characters, and set flag
+    # to use str.isidentifier to validate during lexing
+    from jinja2 import _identifier
+    name_re = re.compile(r'[\w{0}]+'.format(_identifier.pattern))
+    check_ident = True
+    # remove the pattern from memory after building the regex
+    import sys
+    del sys.modules['jinja2._identifier']
+    import jinja2
+    del jinja2._identifier
+    del _identifier
+
+# internal the tokens and keep references to them
+TOKEN_ADD = intern('add')
+TOKEN_ASSIGN = intern('assign')
+TOKEN_COLON = intern('colon')
+TOKEN_COMMA = intern('comma')
+TOKEN_DIV = intern('div')
+TOKEN_DOT = intern('dot')
+TOKEN_EQ = intern('eq')
+TOKEN_FLOORDIV = intern('floordiv')
+TOKEN_GT = intern('gt')
+TOKEN_GTEQ = intern('gteq')
+TOKEN_LBRACE = intern('lbrace')
+TOKEN_LBRACKET = intern('lbracket')
+TOKEN_LPAREN = intern('lparen')
+TOKEN_LT = intern('lt')
+TOKEN_LTEQ = intern('lteq')
+TOKEN_MOD = intern('mod')
+TOKEN_MUL = intern('mul')
+TOKEN_NE = intern('ne')
+TOKEN_PIPE = intern('pipe')
+TOKEN_POW = intern('pow')
+TOKEN_RBRACE = intern('rbrace')
+TOKEN_RBRACKET = intern('rbracket')
+TOKEN_RPAREN = intern('rparen')
+TOKEN_SEMICOLON = intern('semicolon')
+TOKEN_SUB = intern('sub')
+TOKEN_TILDE = intern('tilde')
+TOKEN_WHITESPACE = intern('whitespace')
+TOKEN_FLOAT = intern('float')
+TOKEN_INTEGER = intern('integer')
+TOKEN_NAME = intern('name')
+TOKEN_STRING = intern('string')
+TOKEN_OPERATOR = intern('operator')
+TOKEN_BLOCK_BEGIN = intern('block_begin')
+TOKEN_BLOCK_END = intern('block_end')
+TOKEN_VARIABLE_BEGIN = intern('variable_begin')
+TOKEN_VARIABLE_END = intern('variable_end')
+TOKEN_RAW_BEGIN = intern('raw_begin')
+TOKEN_RAW_END = intern('raw_end')
+TOKEN_COMMENT_BEGIN = intern('comment_begin')
+TOKEN_COMMENT_END = intern('comment_end')
+TOKEN_COMMENT = intern('comment')
+TOKEN_LINESTATEMENT_BEGIN = intern('linestatement_begin')
+TOKEN_LINESTATEMENT_END = intern('linestatement_end')
+TOKEN_LINECOMMENT_BEGIN = intern('linecomment_begin')
+TOKEN_LINECOMMENT_END = intern('linecomment_end')
+TOKEN_LINECOMMENT = intern('linecomment')
+TOKEN_DATA = intern('data')
+TOKEN_INITIAL = intern('initial')
+TOKEN_EOF = intern('eof')
+
+# bind operators to token types
+operators = {
+    '+':            TOKEN_ADD,
+    '-':            TOKEN_SUB,
+    '/':            TOKEN_DIV,
+    '//':           TOKEN_FLOORDIV,
+    '*':            TOKEN_MUL,
+    '%':            TOKEN_MOD,
+    '**':           TOKEN_POW,
+    '~':            TOKEN_TILDE,
+    '[':            TOKEN_LBRACKET,
+    ']':            TOKEN_RBRACKET,
+    '(':            TOKEN_LPAREN,
+    ')':            TOKEN_RPAREN,
+    '{':            TOKEN_LBRACE,
+    '}':            TOKEN_RBRACE,
+    '==':           TOKEN_EQ,
+    '!=':           TOKEN_NE,
+    '>':            TOKEN_GT,
+    '>=':           TOKEN_GTEQ,
+    '<':            TOKEN_LT,
+    '<=':           TOKEN_LTEQ,
+    '=':            TOKEN_ASSIGN,
+    '.':            TOKEN_DOT,
+    ':':            TOKEN_COLON,
+    '|':            TOKEN_PIPE,
+    ',':            TOKEN_COMMA,
+    ';':            TOKEN_SEMICOLON
+}
+
+reverse_operators = dict([(v, k) for k, v in iteritems(operators)])
+assert len(operators) == len(reverse_operators), 'operators dropped'
+operator_re = re.compile('(%s)' % '|'.join(re.escape(x) for x in
+                         sorted(operators, key=lambda x: -len(x))))
+
+ignored_tokens = frozenset([TOKEN_COMMENT_BEGIN, TOKEN_COMMENT,
+                            TOKEN_COMMENT_END, TOKEN_WHITESPACE,
+                            TOKEN_LINECOMMENT_BEGIN, TOKEN_LINECOMMENT_END,
+                            TOKEN_LINECOMMENT])
+ignore_if_empty = frozenset([TOKEN_WHITESPACE, TOKEN_DATA,
+                             TOKEN_COMMENT, TOKEN_LINECOMMENT])
+
+
+def _describe_token_type(token_type):
+    if token_type in reverse_operators:
+        return reverse_operators[token_type]
+    return {
+        TOKEN_COMMENT_BEGIN:        'begin of comment',
+        TOKEN_COMMENT_END:          'end of comment',
+        TOKEN_COMMENT:              'comment',
+        TOKEN_LINECOMMENT:          'comment',
+        TOKEN_BLOCK_BEGIN:          'begin of statement block',
+        TOKEN_BLOCK_END:            'end of statement block',
+        TOKEN_VARIABLE_BEGIN:       'begin of print statement',
+        TOKEN_VARIABLE_END:         'end of print statement',
+        TOKEN_LINESTATEMENT_BEGIN:  'begin of line statement',
+        TOKEN_LINESTATEMENT_END:    'end of line statement',
+        TOKEN_DATA:                 'template data / text',
+        TOKEN_EOF:                  'end of template'
+    }.get(token_type, token_type)
+
+
+def describe_token(token):
+    """Returns a description of the token."""
+    if token.type == TOKEN_NAME:
+        return token.value
+    return _describe_token_type(token.type)
+
+
+def describe_token_expr(expr):
+    """Like `describe_token` but for token expressions."""
+    if ':' in expr:
+        type, value = expr.split(':', 1)
+        if type == TOKEN_NAME:
+            return value
+    else:
+        type = expr
+    return _describe_token_type(type)
+
+
+def count_newlines(value):
+    """Count the number of newline characters in the string.  This is
+    useful for extensions that filter a stream.
+    """
+    return len(newline_re.findall(value))
+
+
+def compile_rules(environment):
+    """Compiles all the rules from the environment into a list of rules."""
+    e = re.escape
+    rules = [
+        (len(environment.comment_start_string), TOKEN_COMMENT_BEGIN,
+         e(environment.comment_start_string)),
+        (len(environment.block_start_string), TOKEN_BLOCK_BEGIN,
+         e(environment.block_start_string)),
+        (len(environment.variable_start_string), TOKEN_VARIABLE_BEGIN,
+         e(environment.variable_start_string))
+    ]
+
+    if environment.line_statement_prefix is not None:
+        rules.append((len(environment.line_statement_prefix), TOKEN_LINESTATEMENT_BEGIN,
+                      r'^[ \t\v]*' + e(environment.line_statement_prefix)))
+    if environment.line_comment_prefix is not None:
+        rules.append((len(environment.line_comment_prefix), TOKEN_LINECOMMENT_BEGIN,
+                      r'(?:^|(?<=\S))[^\S\r\n]*' +
+                      e(environment.line_comment_prefix)))
+
+    return [x[1:] for x in sorted(rules, reverse=True)]
+
+
+class Failure(object):
+    """Class that raises a `TemplateSyntaxError` if called.
+    Used by the `Lexer` to specify known errors.
+    """
+
+    def __init__(self, message, cls=TemplateSyntaxError):
+        self.message = message
+        self.error_class = cls
+
+    def __call__(self, lineno, filename):
+        raise self.error_class(self.message, lineno, filename)
+
+
+class Token(tuple):
+    """Token class."""
+    __slots__ = ()
+    lineno, type, value = (property(itemgetter(x)) for x in range(3))
+
+    def __new__(cls, lineno, type, value):
+        return tuple.__new__(cls, (lineno, intern(str(type)), value))
+
+    def __str__(self):
+        if self.type in reverse_operators:
+            return reverse_operators[self.type]
+        elif self.type == 'name':
+            return self.value
+        return self.type
+
+    def test(self, expr):
+        """Test a token against a token expression.  This can either be a
+        token type or ``'token_type:token_value'``.  This can only test
+        against string values and types.
+        """
+        # here we do a regular string equality check as test_any is usually
+        # passed an iterable of not interned strings.
+        if self.type == expr:
+            return True
+        elif ':' in expr:
+            return expr.split(':', 1) == [self.type, self.value]
+        return False
+
+    def test_any(self, *iterable):
+        """Test against multiple token expressions."""
+        for expr in iterable:
+            if self.test(expr):
+                return True
+        return False
+
+    def __repr__(self):
+        return 'Token(%r, %r, %r)' % (
+            self.lineno,
+            self.type,
+            self.value
+        )
+
+
+@implements_iterator
+class TokenStreamIterator(object):
+    """The iterator for tokenstreams.  Iterate over the stream
+    until the eof token is reached.
+    """
+
+    def __init__(self, stream):
+        self.stream = stream
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        token = self.stream.current
+        if token.type is TOKEN_EOF:
+            self.stream.close()
+            raise StopIteration()
+        next(self.stream)
+        return token
+
+
+@implements_iterator
+class TokenStream(object):
+    """A token stream is an iterable that yields :class:`Token`\\s.  The
+    parser however does not iterate over it but calls :meth:`next` to go
+    one token ahead.  The current active token is stored as :attr:`current`.
+    """
+
+    def __init__(self, generator, name, filename):
+        self._iter = iter(generator)
+        self._pushed = deque()
+        self.name = name
+        self.filename = filename
+        self.closed = False
+        self.current = Token(1, TOKEN_INITIAL, '')
+        next(self)
+
+    def __iter__(self):
+        return TokenStreamIterator(self)
+
+    def __bool__(self):
+        return bool(self._pushed) or self.current.type is not TOKEN_EOF
+    __nonzero__ = __bool__  # py2
+
+    @property
+    def eos(self):
+        """Are we at the end of the stream?"""
+        return not self
+
+    def push(self, token):
+        """Push a token back to the stream."""
+        self._pushed.append(token)
+
+    def look(self):
+        """Look at the next token."""
+        old_token = next(self)
+        result = self.current
+        self.push(result)
+        self.current = old_token
+        return result
+
+    def skip(self, n=1):
+        """Got n tokens ahead."""
+        for x in range(n):
+            next(self)
+
+    def next_if(self, expr):
+        """Perform the token test and return the token if it matched.
+        Otherwise the return value is `None`.
+        """
+        if self.current.test(expr):
+            return next(self)
+
+    def skip_if(self, expr):
+        """Like :meth:`next_if` but only returns `True` or `False`."""
+        return self.next_if(expr) is not None
+
+    def __next__(self):
+        """Go one token ahead and return the old one.
+
+        Use the built-in :func:`next` instead of calling this directly.
+        """
+        rv = self.current
+        if self._pushed:
+            self.current = self._pushed.popleft()
+        elif self.current.type is not TOKEN_EOF:
+            try:
+                self.current = next(self._iter)
+            except StopIteration:
+                self.close()
+        return rv
+
+    def close(self):
+        """Close the stream."""
+        self.current = Token(self.current.lineno, TOKEN_EOF, '')
+        self._iter = None
+        self.closed = True
+
+    def expect(self, expr):
+        """Expect a given token type and return it.  This accepts the same
+        argument as :meth:`jinja2.lexer.Token.test`.
+        """
+        if not self.current.test(expr):
+            expr = describe_token_expr(expr)
+            if self.current.type is TOKEN_EOF:
+                raise TemplateSyntaxError('unexpected end of template, '
+                                          'expected %r.' % expr,
+                                          self.current.lineno,
+                                          self.name, self.filename)
+            raise TemplateSyntaxError("expected token %r, got %r" %
+                                      (expr, describe_token(self.current)),
+                                      self.current.lineno,
+                                      self.name, self.filename)
+        try:
+            return self.current
+        finally:
+            next(self)
+
+
+def get_lexer(environment):
+    """Return a lexer which is probably cached."""
+    key = (environment.block_start_string,
+           environment.block_end_string,
+           environment.variable_start_string,
+           environment.variable_end_string,
+           environment.comment_start_string,
+           environment.comment_end_string,
+           environment.line_statement_prefix,
+           environment.line_comment_prefix,
+           environment.trim_blocks,
+           environment.lstrip_blocks,
+           environment.newline_sequence,
+           environment.keep_trailing_newline)
+    lexer = _lexer_cache.get(key)
+    if lexer is None:
+        lexer = Lexer(environment)
+        _lexer_cache[key] = lexer
+    return lexer
+
+
+class OptionalLStrip(tuple):
+    """A special tuple for marking a point in the state that can have
+    lstrip applied.
+    """
+
+    __slots__ = ()
+
+    # Even though it looks like a no-op, creating instances fails
+    # without this.
+    def __new__(cls, *members, **kwargs):
+        return super(OptionalLStrip, cls).__new__(cls, members)
+
+
+class Lexer(object):
+    """Class that implements a lexer for a given environment. Automatically
+    created by the environment class, usually you don't have to do that.
+
+    Note that the lexer is not automatically bound to an environment.
+    Multiple environments can share the same lexer.
+    """
+
+    def __init__(self, environment):
+        # shortcuts
+        c = lambda x: re.compile(x, re.M | re.S)
+        e = re.escape
+
+        # lexing rules for tags
+        tag_rules = [
+            (whitespace_re, TOKEN_WHITESPACE, None),
+            (float_re, TOKEN_FLOAT, None),
+            (integer_re, TOKEN_INTEGER, None),
+            (name_re, TOKEN_NAME, None),
+            (string_re, TOKEN_STRING, None),
+            (operator_re, TOKEN_OPERATOR, None)
+        ]
+
+        # assemble the root lexing rule. because "|" is ungreedy
+        # we have to sort by length so that the lexer continues working
+        # as expected when we have parsing rules like <% for block and
+        # <%= for variables. (if someone wants asp like syntax)
+        # variables are just part of the rules if variable processing
+        # is required.
+        root_tag_rules = compile_rules(environment)
+
+        # block suffix if trimming is enabled
+        block_suffix_re = environment.trim_blocks and '\\n?' or ''
+
+        # If lstrip is enabled, it should not be applied if there is any
+        # non-whitespace between the newline and block.
+        self.lstrip_unless_re = c(r"[^ \t]") if environment.lstrip_blocks else None
+
+        self.newline_sequence = environment.newline_sequence
+        self.keep_trailing_newline = environment.keep_trailing_newline
+
+        # global lexing rules
+        self.rules = {
+            'root': [
+                # directives
+                (c('(.*?)(?:%s)' % '|'.join(
+                    [r'(?P<raw_begin>%s(\-|\+|)\s*raw\s*(?:\-%s\s*|%s))' % (
+                        e(environment.block_start_string),
+                        e(environment.block_end_string),
+                        e(environment.block_end_string)
+                    )] + [
+                        r'(?P<%s>%s(\-|\+|))' % (n, r)
+                        for n, r in root_tag_rules
+                    ])), OptionalLStrip(TOKEN_DATA, '#bygroup'), '#bygroup'),
+                # data
+                (c('.+'), TOKEN_DATA, None)
+            ],
+            # comments
+            TOKEN_COMMENT_BEGIN: [
+                (c(r'(.*?)((?:\-%s\s*|%s)%s)' % (
+                    e(environment.comment_end_string),
+                    e(environment.comment_end_string),
+                    block_suffix_re
+                )), (TOKEN_COMMENT, TOKEN_COMMENT_END), '#pop'),
+                (c('(.)'), (Failure('Missing end of comment tag'),), None)
+            ],
+            # blocks
+            TOKEN_BLOCK_BEGIN: [
+                (c(r'(?:\-%s\s*|%s)%s' % (
+                    e(environment.block_end_string),
+                    e(environment.block_end_string),
+                    block_suffix_re
+                )), TOKEN_BLOCK_END, '#pop'),
+            ] + tag_rules,
+            # variables
+            TOKEN_VARIABLE_BEGIN: [
+                (c(r'\-%s\s*|%s' % (
+                    e(environment.variable_end_string),
+                    e(environment.variable_end_string)
+                )), TOKEN_VARIABLE_END, '#pop')
+            ] + tag_rules,
+            # raw block
+            TOKEN_RAW_BEGIN: [
+                (c(r'(.*?)((?:%s(\-|\+|))\s*endraw\s*(?:\-%s\s*|%s%s))' % (
+                    e(environment.block_start_string),
+                    e(environment.block_end_string),
+                    e(environment.block_end_string),
+                    block_suffix_re
+                )), OptionalLStrip(TOKEN_DATA, TOKEN_RAW_END), '#pop'),
+                (c('(.)'), (Failure('Missing end of raw directive'),), None)
+            ],
+            # line statements
+            TOKEN_LINESTATEMENT_BEGIN: [
+                (c(r'\s*(\n|$)'), TOKEN_LINESTATEMENT_END, '#pop')
+            ] + tag_rules,
+            # line comments
+            TOKEN_LINECOMMENT_BEGIN: [
+                (c(r'(.*?)()(?=\n|$)'), (TOKEN_LINECOMMENT,
+                 TOKEN_LINECOMMENT_END), '#pop')
+            ]
+        }
+
+    def _normalize_newlines(self, value):
+        """Called for strings and template data to normalize it to unicode."""
+        return newline_re.sub(self.newline_sequence, value)
+
+    def tokenize(self, source, name=None, filename=None, state=None):
+        """Calls tokeniter + tokenize and wraps it in a token stream.
+        """
+        stream = self.tokeniter(source, name, filename, state)
+        return TokenStream(self.wrap(stream, name, filename), name, filename)
+
+    def wrap(self, stream, name=None, filename=None):
+        """This is called with the stream as returned by `tokenize` and wraps
+        every token in a :class:`Token` and converts the value.
+        """
+        for lineno, token, value in stream:
+            if token in ignored_tokens:
+                continue
+            elif token == TOKEN_LINESTATEMENT_BEGIN:
+                token = TOKEN_BLOCK_BEGIN
+            elif token == TOKEN_LINESTATEMENT_END:
+                token = TOKEN_BLOCK_END
+            # we are not interested in those tokens in the parser
+            elif token in (TOKEN_RAW_BEGIN, TOKEN_RAW_END):
+                continue
+            elif token == TOKEN_DATA:
+                value = self._normalize_newlines(value)
+            elif token == 'keyword':
+                token = value
+            elif token == TOKEN_NAME:
+                value = str(value)
+                if check_ident and not value.isidentifier():
+                    raise TemplateSyntaxError(
+                        'Invalid character in identifier',
+                        lineno, name, filename)
+            elif token == TOKEN_STRING:
+                # try to unescape string
+                try:
+                    value = self._normalize_newlines(value[1:-1]) \
+                        .encode('ascii', 'backslashreplace') \
+                        .decode('unicode-escape')
+                except Exception as e:
+                    msg = str(e).split(':')[-1].strip()
+                    raise TemplateSyntaxError(msg, lineno, name, filename)
+            elif token == TOKEN_INTEGER:
+                value = int(value.replace("_", ""))
+            elif token == TOKEN_FLOAT:
+                # remove all "_" first to support more Python versions
+                value = literal_eval(value.replace("_", ""))
+            elif token == TOKEN_OPERATOR:
+                token = operators[value]
+            yield Token(lineno, token, value)
+
+    def tokeniter(self, source, name, filename=None, state=None):
+        """This method tokenizes the text and returns the tokens in a
+        generator.  Use this method if you just want to tokenize a template.
+        """
+        source = text_type(source)
+        lines = source.splitlines()
+        if self.keep_trailing_newline and source:
+            for newline in ('\r\n', '\r', '\n'):
+                if source.endswith(newline):
+                    lines.append('')
+                    break
+        source = '\n'.join(lines)
+        pos = 0
+        lineno = 1
+        stack = ['root']
+        if state is not None and state != 'root':
+            assert state in ('variable', 'block'), 'invalid state'
+            stack.append(state + '_begin')
+        statetokens = self.rules[stack[-1]]
+        source_length = len(source)
+        balancing_stack = []
+        lstrip_unless_re = self.lstrip_unless_re
+
+        while 1:
+            # tokenizer loop
+            for regex, tokens, new_state in statetokens:
+                m = regex.match(source, pos)
+                # if no match we try again with the next rule
+                if m is None:
+                    continue
+
+                # we only match blocks and variables if braces / parentheses
+                # are balanced. continue parsing with the lower rule which
+                # is the operator rule. do this only if the end tags look
+                # like operators
+                if (
+                    balancing_stack
+                    and tokens in (
+                        TOKEN_VARIABLE_END, TOKEN_BLOCK_END, TOKEN_LINESTATEMENT_END
+                    )
+                ):
+                    continue
+
+                # tuples support more options
+                if isinstance(tokens, tuple):
+                    groups = m.groups()
+
+                    if isinstance(tokens, OptionalLStrip):
+                        # Rule supports lstrip. Match will look like
+                        # text, block type, whitespace control, type, control, ...
+                        text = groups[0]
+
+                        # Skipping the text and first type, every other group is the
+                        # whitespace control for each type. One of the groups will be
+                        # -, +, or empty string instead of None.
+                        strip_sign = next(g for g in groups[2::2] if g is not None)
+
+                        if strip_sign == "-":
+                            # Strip all whitespace between the text and the tag.
+                            groups = (text.rstrip(),) + groups[1:]
+                        elif (
+                            # Not marked for preserving whitespace.
+                            strip_sign != "+"
+                            # lstrip is enabled.
+                            and lstrip_unless_re is not None
+                            # Not a variable expression.
+                            and not m.groupdict().get(TOKEN_VARIABLE_BEGIN)
+                        ):
+                            # The start of text between the last newline and the tag.
+                            l_pos = text.rfind('\n') + 1
+
+                            # If there's only whitespace between the newline and the
+                            # tag, strip it.
+                            if not lstrip_unless_re.search(text, l_pos):
+                                groups = (text[:l_pos],) + groups[1:]
+
+                    for idx, token in enumerate(tokens):
+                        # failure group
+                        if token.__class__ is Failure:
+                            raise token(lineno, filename)
+                        # bygroup is a bit more complex, in that case we
+                        # yield for the current token the first named
+                        # group that matched
+                        elif token == '#bygroup':
+                            for key, value in iteritems(m.groupdict()):
+                                if value is not None:
+                                    yield lineno, key, value
+                                    lineno += value.count('\n')
+                                    break
+                            else:
+                                raise RuntimeError('%r wanted to resolve '
+                                                   'the token dynamically'
+                                                   ' but no group matched'
+                                                   % regex)
+                        # normal group
+                        else:
+                            data = groups[idx]
+                            if data or token not in ignore_if_empty:
+                                yield lineno, token, data
+                            lineno += data.count('\n')
+
+                # strings as token just are yielded as it.
+                else:
+                    data = m.group()
+                    # update brace/parentheses balance
+                    if tokens == TOKEN_OPERATOR:
+                        if data == '{':
+                            balancing_stack.append('}')
+                        elif data == '(':
+                            balancing_stack.append(')')
+                        elif data == '[':
+                            balancing_stack.append(']')
+                        elif data in ('}', ')', ']'):
+                            if not balancing_stack:
+                                raise TemplateSyntaxError('unexpected \'%s\'' %
+                                                          data, lineno, name,
+                                                          filename)
+                            expected_op = balancing_stack.pop()
+                            if expected_op != data:
+                                raise TemplateSyntaxError('unexpected \'%s\', '
+                                                          'expected \'%s\'' %
+                                                          (data, expected_op),
+                                                          lineno, name,
+                                                          filename)
+                    # yield items
+                    if data or tokens not in ignore_if_empty:
+                        yield lineno, tokens, data
+                    lineno += data.count('\n')
+
+                # fetch new position into new variable so that we can check
+                # if there is a internal parsing error which would result
+                # in an infinite loop
+                pos2 = m.end()
+
+                # handle state changes
+                if new_state is not None:
+                    # remove the uppermost state
+                    if new_state == '#pop':
+                        stack.pop()
+                    # resolve the new state by group checking
+                    elif new_state == '#bygroup':
+                        for key, value in iteritems(m.groupdict()):
+                            if value is not None:
+                                stack.append(key)
+                                break
+                        else:
+                            raise RuntimeError('%r wanted to resolve the '
+                                               'new state dynamically but'
+                                               ' no group matched' %
+                                               regex)
+                    # direct state name given
+                    else:
+                        stack.append(new_state)
+                    statetokens = self.rules[stack[-1]]
+                # we are still at the same position and no stack change.
+                # this means a loop without break condition, avoid that and
+                # raise error
+                elif pos2 == pos:
+                    raise RuntimeError('%r yielded empty string without '
+                                       'stack change' % regex)
+                # publish new function and start again
+                pos = pos2
+                break
+            # if loop terminated without break we haven't found a single match
+            # either we are at the end of the file or we have a problem
+            else:
+                # end of text
+                if pos >= source_length:
+                    return
+                # something went wrong
+                raise TemplateSyntaxError('unexpected char %r at %d' %
+                                          (source[pos], pos), lineno,
+                                          name, filename)
diff --git a/src/jinja2/loaders.py b/src/jinja2/loaders.py
new file mode 100644
index 0000000..cc269be
--- /dev/null
+++ b/src/jinja2/loaders.py
@@ -0,0 +1,567 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.loaders
+    ~~~~~~~~~~~~~~
+
+    Jinja loader classes.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import os
+import pkgutil
+import sys
+import weakref
+from importlib import import_module
+from types import ModuleType
+from os import path
+from hashlib import sha1
+from jinja2.exceptions import TemplateNotFound
+from jinja2.utils import open_if_exists, internalcode
+from jinja2._compat import string_types, iteritems, fspath, abc
+
+
+def split_template_path(template):
+    """Split a path into segments and perform a sanity check.  If it detects
+    '..' in the path it will raise a `TemplateNotFound` error.
+    """
+    pieces = []
+    for piece in template.split('/'):
+        if path.sep in piece \
+           or (path.altsep and path.altsep in piece) or \
+           piece == path.pardir:
+            raise TemplateNotFound(template)
+        elif piece and piece != '.':
+            pieces.append(piece)
+    return pieces
+
+
+class BaseLoader(object):
+    """Baseclass for all loaders.  Subclass this and override `get_source` to
+    implement a custom loading mechanism.  The environment provides a
+    `get_template` method that calls the loader's `load` method to get the
+    :class:`Template` object.
+
+    A very basic example for a loader that looks up templates on the file
+    system could look like this::
+
+        from jinja2 import BaseLoader, TemplateNotFound
+        from os.path import join, exists, getmtime
+
+        class MyLoader(BaseLoader):
+
+            def __init__(self, path):
+                self.path = path
+
+            def get_source(self, environment, template):
+                path = join(self.path, template)
+                if not exists(path):
+                    raise TemplateNotFound(template)
+                mtime = getmtime(path)
+                with file(path) as f:
+                    source = f.read().decode('utf-8')
+                return source, path, lambda: mtime == getmtime(path)
+    """
+
+    #: if set to `False` it indicates that the loader cannot provide access
+    #: to the source of templates.
+    #:
+    #: .. versionadded:: 2.4
+    has_source_access = True
+
+    def get_source(self, environment, template):
+        """Get the template source, filename and reload helper for a template.
+        It's passed the environment and template name and has to return a
+        tuple in the form ``(source, filename, uptodate)`` or raise a
+        `TemplateNotFound` error if it can't locate the template.
+
+        The source part of the returned tuple must be the source of the
+        template as unicode string or a ASCII bytestring.  The filename should
+        be the name of the file on the filesystem if it was loaded from there,
+        otherwise `None`.  The filename is used by python for the tracebacks
+        if no loader extension is used.
+
+        The last item in the tuple is the `uptodate` function.  If auto
+        reloading is enabled it's always called to check if the template
+        changed.  No arguments are passed so the function must store the
+        old state somewhere (for example in a closure).  If it returns `False`
+        the template will be reloaded.
+        """
+        if not self.has_source_access:
+            raise RuntimeError('%s cannot provide access to the source' %
+                               self.__class__.__name__)
+        raise TemplateNotFound(template)
+
+    def list_templates(self):
+        """Iterates over all templates.  If the loader does not support that
+        it should raise a :exc:`TypeError` which is the default behavior.
+        """
+        raise TypeError('this loader cannot iterate over all templates')
+
+    @internalcode
+    def load(self, environment, name, globals=None):
+        """Loads a template.  This method looks up the template in the cache
+        or loads one by calling :meth:`get_source`.  Subclasses should not
+        override this method as loaders working on collections of other
+        loaders (such as :class:`PrefixLoader` or :class:`ChoiceLoader`)
+        will not call this method but `get_source` directly.
+        """
+        code = None
+        if globals is None:
+            globals = {}
+
+        # first we try to get the source for this template together
+        # with the filename and the uptodate function.
+        source, filename, uptodate = self.get_source(environment, name)
+
+        # try to load the code from the bytecode cache if there is a
+        # bytecode cache configured.
+        bcc = environment.bytecode_cache
+        if bcc is not None:
+            bucket = bcc.get_bucket(environment, name, filename, source)
+            code = bucket.code
+
+        # if we don't have code so far (not cached, no longer up to
+        # date) etc. we compile the template
+        if code is None:
+            code = environment.compile(source, name, filename)
+
+        # if the bytecode cache is available and the bucket doesn't
+        # have a code so far, we give the bucket the new code and put
+        # it back to the bytecode cache.
+        if bcc is not None and bucket.code is None:
+            bucket.code = code
+            bcc.set_bucket(bucket)
+
+        return environment.template_class.from_code(environment, code,
+                                                    globals, uptodate)
+
+
+class FileSystemLoader(BaseLoader):
+    """Loads templates from the file system.  This loader can find templates
+    in folders on the file system and is the preferred way to load them.
+
+    The loader takes the path to the templates as string, or if multiple
+    locations are wanted a list of them which is then looked up in the
+    given order::
+
+    >>> loader = FileSystemLoader('/path/to/templates')
+    >>> loader = FileSystemLoader(['/path/to/templates', '/other/path'])
+
+    Per default the template encoding is ``'utf-8'`` which can be changed
+    by setting the `encoding` parameter to something else.
+
+    To follow symbolic links, set the *followlinks* parameter to ``True``::
+
+    >>> loader = FileSystemLoader('/path/to/templates', followlinks=True)
+
+    .. versionchanged:: 2.8
+       The ``followlinks`` parameter was added.
+    """
+
+    def __init__(self, searchpath, encoding='utf-8', followlinks=False):
+        if (
+            not isinstance(searchpath, abc.Iterable)
+            or isinstance(searchpath, string_types)
+        ):
+            searchpath = [searchpath]
+
+        # In Python 3.5, os.path.join doesn't support Path. This can be
+        # simplified to list(searchpath) when Python 3.5 is dropped.
+        self.searchpath = [fspath(p) for p in searchpath]
+
+        self.encoding = encoding
+        self.followlinks = followlinks
+
+    def get_source(self, environment, template):
+        pieces = split_template_path(template)
+        for searchpath in self.searchpath:
+            filename = path.join(searchpath, *pieces)
+            f = open_if_exists(filename)
+            if f is None:
+                continue
+            try:
+                contents = f.read().decode(self.encoding)
+            finally:
+                f.close()
+
+            mtime = path.getmtime(filename)
+
+            def uptodate():
+                try:
+                    return path.getmtime(filename) == mtime
+                except OSError:
+                    return False
+            return contents, filename, uptodate
+        raise TemplateNotFound(template)
+
+    def list_templates(self):
+        found = set()
+        for searchpath in self.searchpath:
+            walk_dir = os.walk(searchpath, followlinks=self.followlinks)
+            for dirpath, dirnames, filenames in walk_dir:
+                for filename in filenames:
+                    template = os.path.join(dirpath, filename) \
+                        [len(searchpath):].strip(os.path.sep) \
+                                          .replace(os.path.sep, '/')
+                    if template[:2] == './':
+                        template = template[2:]
+                    if template not in found:
+                        found.add(template)
+        return sorted(found)
+
+
+class PackageLoader(BaseLoader):
+    """Load templates from a directory in a Python package.
+
+    :param package_name: Import name of the package that contains the
+        template directory.
+    :param package_path: Directory within the imported package that
+        contains the templates.
+    :param encoding: Encoding of template files.
+
+    The following example looks up templates in the ``pages`` directory
+    within the ``project.ui`` package.
+
+    .. code-block:: python
+
+        loader = PackageLoader("project.ui", "pages")
+
+    Only packages installed as directories (standard pip behavior) or
+    zip/egg files (less common) are supported. The Python API for
+    introspecting data in packages is too limited to support other
+    installation methods the way this loader requires.
+
+    There is limited support for :pep:`420` namespace packages. The
+    template directory is assumed to only be in one namespace
+    contributor. Zip files contributing to a namespace are not
+    supported.
+
+    .. versionchanged:: 2.11.0
+        No longer uses ``setuptools`` as a dependency.
+
+    .. versionchanged:: 2.11.0
+        Limited PEP 420 namespace package support.
+    """
+
+    def __init__(self, package_name, package_path="templates", encoding="utf-8"):
+        if package_path == os.path.curdir:
+            package_path = ""
+        elif package_path[:2] == os.path.curdir + os.path.sep:
+            package_path = package_path[2:]
+
+        package_path = os.path.normpath(package_path).rstrip(os.path.sep)
+        self.package_path = package_path
+        self.package_name = package_name
+        self.encoding = encoding
+
+        # Make sure the package exists. This also makes namespace
+        # packages work, otherwise get_loader returns None.
+        import_module(package_name)
+        self._loader = loader = pkgutil.get_loader(package_name)
+
+        # Zip loader's archive attribute points at the zip.
+        self._archive = getattr(loader, "archive", None)
+        self._template_root = None
+
+        if hasattr(loader, "get_filename"):
+            # A standard directory package, or a zip package.
+            self._template_root = os.path.join(
+                os.path.dirname(loader.get_filename(package_name)), package_path
+            )
+        elif hasattr(loader, "_path"):
+            # A namespace package, limited support. Find the first
+            # contributor with the template directory.
+            for root in loader._path:
+                root = os.path.join(root, package_path)
+
+                if os.path.isdir(root):
+                    self._template_root = root
+                    break
+
+        if self._template_root is None:
+            raise ValueError(
+                "The %r package was not installed in a way that"
+                " PackageLoader understands." % package_name
+            )
+
+    def get_source(self, environment, template):
+        p = os.path.join(self._template_root, *split_template_path(template))
+
+        if self._archive is None:
+            # Package is a directory.
+            if not os.path.isfile(p):
+                raise TemplateNotFound(template)
+
+            with open(p, "rb") as f:
+                source = f.read()
+
+            mtime = os.path.getmtime(p)
+
+            def up_to_date():
+                return os.path.isfile(p) and os.path.getmtime(p) == mtime
+        else:
+            # Package is a zip file.
+            try:
+                source = self._loader.get_data(p)
+            except OSError:
+                raise TemplateNotFound(template)
+
+            # Could use the zip's mtime for all template mtimes, but
+            # would need to safely reload the module if it's out of
+            # date, so just report it as always current.
+            up_to_date = None
+
+        return source.decode(self.encoding), p, up_to_date
+
+    def list_templates(self):
+        results = []
+
+        if self._archive is None:
+            # Package is a directory.
+            offset = len(self._template_root)
+
+            for dirpath, _, filenames in os.walk(self._template_root):
+                dirpath = dirpath[offset:].lstrip(os.path.sep)
+                results.extend(
+                    os.path.join(dirpath, name).replace(os.path.sep, "/")
+                    for name in filenames
+                )
+        else:
+            if not hasattr(self._loader, "_files"):
+                raise TypeError(
+                    "This zip import does not have the required"
+                    " metadata to list templates."
+                )
+
+            # Package is a zip file.
+            prefix = (
+                self._template_root[len(self._archive):].lstrip(os.path.sep)
+                + os.path.sep
+            )
+            offset = len(prefix)
+
+            for name in self._loader._files.keys():
+                # Find names under the templates directory that aren't directories.
+                if name.startswith(prefix) and name[-1] != os.path.sep:
+                    results.append(name[offset:].replace(os.path.sep, "/"))
+
+        results.sort()
+        return results
+
+
+class DictLoader(BaseLoader):
+    """Loads a template from a python dict.  It's passed a dict of unicode
+    strings bound to template names.  This loader is useful for unittesting:
+
+    >>> loader = DictLoader({'index.html': 'source here'})
+
+    Because auto reloading is rarely useful this is disabled per default.
+    """
+
+    def __init__(self, mapping):
+        self.mapping = mapping
+
+    def get_source(self, environment, template):
+        if template in self.mapping:
+            source = self.mapping[template]
+            return source, None, lambda: source == self.mapping.get(template)
+        raise TemplateNotFound(template)
+
+    def list_templates(self):
+        return sorted(self.mapping)
+
+
+class FunctionLoader(BaseLoader):
+    """A loader that is passed a function which does the loading.  The
+    function receives the name of the template and has to return either
+    an unicode string with the template source, a tuple in the form ``(source,
+    filename, uptodatefunc)`` or `None` if the template does not exist.
+
+    >>> def load_template(name):
+    ...     if name == 'index.html':
+    ...         return '...'
+    ...
+    >>> loader = FunctionLoader(load_template)
+
+    The `uptodatefunc` is a function that is called if autoreload is enabled
+    and has to return `True` if the template is still up to date.  For more
+    details have a look at :meth:`BaseLoader.get_source` which has the same
+    return value.
+    """
+
+    def __init__(self, load_func):
+        self.load_func = load_func
+
+    def get_source(self, environment, template):
+        rv = self.load_func(template)
+        if rv is None:
+            raise TemplateNotFound(template)
+        elif isinstance(rv, string_types):
+            return rv, None, None
+        return rv
+
+
+class PrefixLoader(BaseLoader):
+    """A loader that is passed a dict of loaders where each loader is bound
+    to a prefix.  The prefix is delimited from the template by a slash per
+    default, which can be changed by setting the `delimiter` argument to
+    something else::
+
+        loader = PrefixLoader({
+            'app1':     PackageLoader('mypackage.app1'),
+            'app2':     PackageLoader('mypackage.app2')
+        })
+
+    By loading ``'app1/index.html'`` the file from the app1 package is loaded,
+    by loading ``'app2/index.html'`` the file from the second.
+    """
+
+    def __init__(self, mapping, delimiter='/'):
+        self.mapping = mapping
+        self.delimiter = delimiter
+
+    def get_loader(self, template):
+        try:
+            prefix, name = template.split(self.delimiter, 1)
+            loader = self.mapping[prefix]
+        except (ValueError, KeyError):
+            raise TemplateNotFound(template)
+        return loader, name
+
+    def get_source(self, environment, template):
+        loader, name = self.get_loader(template)
+        try:
+            return loader.get_source(environment, name)
+        except TemplateNotFound:
+            # re-raise the exception with the correct filename here.
+            # (the one that includes the prefix)
+            raise TemplateNotFound(template)
+
+    @internalcode
+    def load(self, environment, name, globals=None):
+        loader, local_name = self.get_loader(name)
+        try:
+            return loader.load(environment, local_name, globals)
+        except TemplateNotFound:
+            # re-raise the exception with the correct filename here.
+            # (the one that includes the prefix)
+            raise TemplateNotFound(name)
+
+    def list_templates(self):
+        result = []
+        for prefix, loader in iteritems(self.mapping):
+            for template in loader.list_templates():
+                result.append(prefix + self.delimiter + template)
+        return result
+
+
+class ChoiceLoader(BaseLoader):
+    """This loader works like the `PrefixLoader` just that no prefix is
+    specified.  If a template could not be found by one loader the next one
+    is tried.
+
+    >>> loader = ChoiceLoader([
+    ...     FileSystemLoader('/path/to/user/templates'),
+    ...     FileSystemLoader('/path/to/system/templates')
+    ... ])
+
+    This is useful if you want to allow users to override builtin templates
+    from a different location.
+    """
+
+    def __init__(self, loaders):
+        self.loaders = loaders
+
+    def get_source(self, environment, template):
+        for loader in self.loaders:
+            try:
+                return loader.get_source(environment, template)
+            except TemplateNotFound:
+                pass
+        raise TemplateNotFound(template)
+
+    @internalcode
+    def load(self, environment, name, globals=None):
+        for loader in self.loaders:
+            try:
+                return loader.load(environment, name, globals)
+            except TemplateNotFound:
+                pass
+        raise TemplateNotFound(name)
+
+    def list_templates(self):
+        found = set()
+        for loader in self.loaders:
+            found.update(loader.list_templates())
+        return sorted(found)
+
+
+class _TemplateModule(ModuleType):
+    """Like a normal module but with support for weak references"""
+
+
+class ModuleLoader(BaseLoader):
+    """This loader loads templates from precompiled templates.
+
+    Example usage:
+
+    >>> loader = ChoiceLoader([
+    ...     ModuleLoader('/path/to/compiled/templates'),
+    ...     FileSystemLoader('/path/to/templates')
+    ... ])
+
+    Templates can be precompiled with :meth:`Environment.compile_templates`.
+    """
+
+    has_source_access = False
+
+    def __init__(self, path):
+        package_name = '_jinja2_module_templates_%x' % id(self)
+
+        # create a fake module that looks for the templates in the
+        # path given.
+        mod = _TemplateModule(package_name)
+
+        if (
+            not isinstance(path, abc.Iterable)
+            or isinstance(path, string_types)
+        ):
+            path = [path]
+
+        mod.__path__ = [fspath(p) for p in path]
+
+        sys.modules[package_name] = weakref.proxy(mod,
+            lambda x: sys.modules.pop(package_name, None))
+
+        # the only strong reference, the sys.modules entry is weak
+        # so that the garbage collector can remove it once the
+        # loader that created it goes out of business.
+        self.module = mod
+        self.package_name = package_name
+
+    @staticmethod
+    def get_template_key(name):
+        return 'tmpl_' + sha1(name.encode('utf-8')).hexdigest()
+
+    @staticmethod
+    def get_module_filename(name):
+        return ModuleLoader.get_template_key(name) + '.py'
+
+    @internalcode
+    def load(self, environment, name, globals=None):
+        key = self.get_template_key(name)
+        module = '%s.%s' % (self.package_name, key)
+        mod = getattr(self.module, module, None)
+        if mod is None:
+            try:
+                mod = __import__(module, None, None, ['root'])
+            except ImportError:
+                raise TemplateNotFound(name)
+
+            # remove the entry from sys.modules, we only want the attribute
+            # on the module object we have stored on the loader.
+            sys.modules.pop(module, None)
+
+        return environment.template_class.from_module_dict(
+            environment, mod.__dict__, globals)
diff --git a/src/jinja2/meta.py b/src/jinja2/meta.py
new file mode 100644
index 0000000..0d25916
--- /dev/null
+++ b/src/jinja2/meta.py
@@ -0,0 +1,106 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.meta
+    ~~~~~~~~~~~
+
+    This module implements various functions that exposes information about
+    templates that might be interesting for various kinds of applications.
+
+    :copyright: (c) 2017 by the Jinja Team, see AUTHORS for more details.
+    :license: BSD, see LICENSE for more details.
+"""
+from jinja2 import nodes
+from jinja2.compiler import CodeGenerator
+from jinja2._compat import string_types, iteritems
+
+
+class TrackingCodeGenerator(CodeGenerator):
+    """We abuse the code generator for introspection."""
+
+    def __init__(self, environment):
+        CodeGenerator.__init__(self, environment, '<introspection>',
+                               '<introspection>')
+        self.undeclared_identifiers = set()
+
+    def write(self, x):
+        """Don't write."""
+
+    def enter_frame(self, frame):
+        """Remember all undeclared identifiers."""
+        CodeGenerator.enter_frame(self, frame)
+        for _, (action, param) in iteritems(frame.symbols.loads):
+            if action == 'resolve' and param not in self.environment.globals:
+                self.undeclared_identifiers.add(param)
+
+
+def find_undeclared_variables(ast):
+    """Returns a set of all variables in the AST that will be looked up from
+    the context at runtime.  Because at compile time it's not known which
+    variables will be used depending on the path the execution takes at
+    runtime, all variables are returned.
+
+    >>> from jinja2 import Environment, meta
+    >>> env = Environment()
+    >>> ast = env.parse('{% set foo = 42 %}{{ bar + foo }}')
+    >>> meta.find_undeclared_variables(ast) == set(['bar'])
+    True
+
+    .. admonition:: Implementation
+
+       Internally the code generator is used for finding undeclared variables.
+       This is good to know because the code generator might raise a
+       :exc:`TemplateAssertionError` during compilation and as a matter of
+       fact this function can currently raise that exception as well.
+    """
+    codegen = TrackingCodeGenerator(ast.environment)
+    codegen.visit(ast)
+    return codegen.undeclared_identifiers
+
+
+def find_referenced_templates(ast):
+    """Finds all the referenced templates from the AST.  This will return an
+    iterator over all the hardcoded template extensions, inclusions and
+    imports.  If dynamic inheritance or inclusion is used, `None` will be
+    yielded.
+
+    >>> from jinja2 import Environment, meta
+    >>> env = Environment()
+    >>> ast = env.parse('{% extends "layout.html" %}{% include helper %}')
+    >>> list(meta.find_referenced_templates(ast))
+    ['layout.html', None]
+
+    This function is useful for dependency tracking.  For example if you want
+    to rebuild parts of the website after a layout template has changed.
+    """
+    for node in ast.find_all((nodes.Extends, nodes.FromImport, nodes.Import,
+                              nodes.Include)):
+        if not isinstance(node.template, nodes.Const):
+            # a tuple with some non consts in there
+            if isinstance(node.template, (nodes.Tuple, nodes.List)):
+                for template_name in node.template.items:
+                    # something const, only yield the strings and ignore
+                    # non-string consts that really just make no sense
+                    if isinstance(template_name, nodes.Const):
+                        if isinstance(template_name.value, string_types):
+                            yield template_name.value
+                    # something dynamic in there
+                    else:
+                        yield None
+            # something dynamic we don't know about here
+            else:
+                yield None
+            continue
+        # constant is a basestring, direct template name
+        if isinstance(node.template.value, string_types):
+            yield node.template.value
+        # a tuple or list (latter *should* not happen) made of consts,
+        # yield the consts that are strings.  We could warn here for
+        # non string values
+        elif isinstance(node, nodes.Include) and \
+             isinstance(node.template.value, (tuple, list)):
+            for template_name in node.template.value:
+                if isinstance(template_name, string_types):
+                    yield template_name
+        # something else we don't care about, we could warn here
+        else:
+            yield None
diff --git a/src/jinja2/nativetypes.py b/src/jinja2/nativetypes.py
new file mode 100644
index 0000000..e0de277
--- /dev/null
+++ b/src/jinja2/nativetypes.py
@@ -0,0 +1,107 @@
+import types
+from ast import literal_eval
+from itertools import islice, chain
+from jinja2 import nodes
+from jinja2._compat import text_type
+from jinja2.compiler import CodeGenerator, has_safe_repr
+from jinja2.environment import Environment, Template
+
+
+def native_concat(nodes, preserve_quotes=True):
+    """Return a native Python type from the list of compiled nodes. If
+    the result is a single node, its value is returned. Otherwise, the
+    nodes are concatenated as strings. If the result can be parsed with
+    :func:`ast.literal_eval`, the parsed value is returned. Otherwise,
+    the string is returned.
+
+    :param nodes: Iterable of nodes to concatenate.
+    :param preserve_quotes: Whether to re-wrap literal strings with
+        quotes, to preserve quotes around expressions for later parsing.
+        Should be ``False`` in :meth:`NativeEnvironment.render`.
+    """
+    head = list(islice(nodes, 2))
+
+    if not head:
+        return None
+
+    if len(head) == 1:
+        raw = head[0]
+    else:
+        if isinstance(nodes, types.GeneratorType):
+            nodes = chain(head, nodes)
+        raw = u''.join([text_type(v) for v in nodes])
+
+    try:
+        literal = literal_eval(raw)
+    except (ValueError, SyntaxError, MemoryError):
+        return raw
+
+    # If literal_eval returned a string, re-wrap with the original
+    # quote character to avoid dropping quotes between expression nodes.
+    # Without this, "'{{ a }}', '{{ b }}'" results in "a, b", but should
+    # be ('a', 'b').
+    if preserve_quotes and isinstance(literal, str):
+        return "{quote}{}{quote}".format(literal, quote=raw[0])
+
+    return literal
+
+
+class NativeCodeGenerator(CodeGenerator):
+    """A code generator which renders Python types by not adding
+    ``to_string()`` around output nodes, and using :func:`native_concat`
+    to convert complex strings back to Python types if possible.
+    """
+
+    @staticmethod
+    def _default_finalize(value):
+        return value
+
+    def _output_const_repr(self, group):
+        return repr(native_concat(group))
+
+    def _output_child_to_const(self, node, frame, finalize):
+        const = node.as_const(frame.eval_ctx)
+
+        if not has_safe_repr(const):
+            raise nodes.Impossible()
+
+        if isinstance(node, nodes.TemplateData):
+            return const
+
+        return finalize.const(const)
+
+    def _output_child_pre(self, node, frame, finalize):
+        if finalize.src is not None:
+            self.write(finalize.src)
+
+    def _output_child_post(self, node, frame, finalize):
+        if finalize.src is not None:
+            self.write(")")
+
+
+class NativeEnvironment(Environment):
+    """An environment that renders templates to native Python types."""
+
+    code_generator_class = NativeCodeGenerator
+
+
+class NativeTemplate(Template):
+    environment_class = NativeEnvironment
+
+    def render(self, *args, **kwargs):
+        """Render the template to produce a native Python type. If the
+        result is a single node, its value is returned. Otherwise, the
+        nodes are concatenated as strings. If the result can be parsed
+        with :func:`ast.literal_eval`, the parsed value is returned.
+        Otherwise, the string is returned.
+        """
+        vars = dict(*args, **kwargs)
+        try:
+            return native_concat(
+                self.root_render_func(self.new_context(vars)), preserve_quotes=False
+            )
+        except Exception:
+            return self.environment.handle_exception()
+
+
+NativeEnvironment.template_class = NativeTemplate
diff --git a/src/jinja2/nodes.py b/src/jinja2/nodes.py
new file mode 100644
index 0000000..00e0329
--- /dev/null
+++ b/src/jinja2/nodes.py
@@ -0,0 +1,1015 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.nodes
+    ~~~~~~~~~~~~
+
+    This module implements additional nodes derived from the ast base node.
+
+    It also provides some node tree helper functions like `in_lineno` and
+    `get_nodes` used by the parser and translator in order to normalize
+    python and jinja nodes.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import types
+import operator
+
+from collections import deque
+from jinja2.utils import Markup
+from jinja2._compat import izip, with_metaclass, text_type, PY2
+
+
+_binop_to_func = {
+    '*':        operator.mul,
+    '/':        operator.truediv,
+    '//':       operator.floordiv,
+    '**':       operator.pow,
+    '%':        operator.mod,
+    '+':        operator.add,
+    '-':        operator.sub
+}
+
+_uaop_to_func = {
+    'not':      operator.not_,
+    '+':        operator.pos,
+    '-':        operator.neg
+}
+
+_cmpop_to_func = {
+    'eq':       operator.eq,
+    'ne':       operator.ne,
+    'gt':       operator.gt,
+    'gteq':     operator.ge,
+    'lt':       operator.lt,
+    'lteq':     operator.le,
+    'in':       lambda a, b: a in b,
+    'notin':    lambda a, b: a not in b
+}
+
+
+class Impossible(Exception):
+    """Raised if the node could not perform a requested action."""
+
+
+class NodeType(type):
+    """A metaclass for nodes that handles the field and attribute
+    inheritance.  fields and attributes from the parent class are
+    automatically forwarded to the child."""
+
+    def __new__(cls, name, bases, d):
+        for attr in 'fields', 'attributes':
+            storage = []
+            storage.extend(getattr(bases[0], attr, ()))
+            storage.extend(d.get(attr, ()))
+            assert len(bases) == 1, 'multiple inheritance not allowed'
+            assert len(storage) == len(set(storage)), 'layout conflict'
+            d[attr] = tuple(storage)
+        d.setdefault('abstract', False)
+        return type.__new__(cls, name, bases, d)
+
+
+class EvalContext(object):
+    """Holds evaluation time information.  Custom attributes can be attached
+    to it in extensions.
+    """
+
+    def __init__(self, environment, template_name=None):
+        self.environment = environment
+        if callable(environment.autoescape):
+            self.autoescape = environment.autoescape(template_name)
+        else:
+            self.autoescape = environment.autoescape
+        self.volatile = False
+
+    def save(self):
+        return self.__dict__.copy()
+
+    def revert(self, old):
+        self.__dict__.clear()
+        self.__dict__.update(old)
+
+
+def get_eval_context(node, ctx):
+    if ctx is None:
+        if node.environment is None:
+            raise RuntimeError('if no eval context is passed, the '
+                               'node must have an attached '
+                               'environment.')
+        return EvalContext(node.environment)
+    return ctx
+
+
+class Node(with_metaclass(NodeType, object)):
+    """Baseclass for all Jinja nodes.  There are a number of nodes available
+    of different types.  There are four major types:
+
+    -   :class:`Stmt`: statements
+    -   :class:`Expr`: expressions
+    -   :class:`Helper`: helper nodes
+    -   :class:`Template`: the outermost wrapper node
+
+    All nodes have fields and attributes.  Fields may be other nodes, lists,
+    or arbitrary values.  Fields are passed to the constructor as regular
+    positional arguments, attributes as keyword arguments.  Each node has
+    two attributes: `lineno` (the line number of the node) and `environment`.
+    The `environment` attribute is set at the end of the parsing process for
+    all nodes automatically.
+    """
+    fields = ()
+    attributes = ('lineno', 'environment')
+    abstract = True
+
+    def __init__(self, *fields, **attributes):
+        if self.abstract:
+            raise TypeError('abstract nodes are not instantiable')
+        if fields:
+            if len(fields) != len(self.fields):
+                if not self.fields:
+                    raise TypeError('%r takes 0 arguments' %
+                                    self.__class__.__name__)
+                raise TypeError('%r takes 0 or %d argument%s' % (
+                    self.__class__.__name__,
+                    len(self.fields),
+                    len(self.fields) != 1 and 's' or ''
+                ))
+            for name, arg in izip(self.fields, fields):
+                setattr(self, name, arg)
+        for attr in self.attributes:
+            setattr(self, attr, attributes.pop(attr, None))
+        if attributes:
+            raise TypeError('unknown attribute %r' %
+                            next(iter(attributes)))
+
+    def iter_fields(self, exclude=None, only=None):
+        """This method iterates over all fields that are defined and yields
+        ``(key, value)`` tuples.  Per default all fields are returned, but
+        it's possible to limit that to some fields by providing the `only`
+        parameter or to exclude some using the `exclude` parameter.  Both
+        should be sets or tuples of field names.
+        """
+        for name in self.fields:
+            if (exclude is only is None) or \
+               (exclude is not None and name not in exclude) or \
+               (only is not None and name in only):
+                try:
+                    yield name, getattr(self, name)
+                except AttributeError:
+                    pass
+
+    def iter_child_nodes(self, exclude=None, only=None):
+        """Iterates over all direct child nodes of the node.  This iterates
+        over all fields and yields the values of they are nodes.  If the value
+        of a field is a list all the nodes in that list are returned.
+        """
+        for field, item in self.iter_fields(exclude, only):
+            if isinstance(item, list):
+                for n in item:
+                    if isinstance(n, Node):
+                        yield n
+            elif isinstance(item, Node):
+                yield item
+
+    def find(self, node_type):
+        """Find the first node of a given type.  If no such node exists the
+        return value is `None`.
+        """
+        for result in self.find_all(node_type):
+            return result
+
+    def find_all(self, node_type):
+        """Find all the nodes of a given type.  If the type is a tuple,
+        the check is performed for any of the tuple items.
+        """
+        for child in self.iter_child_nodes():
+            if isinstance(child, node_type):
+                yield child
+            for result in child.find_all(node_type):
+                yield result
+
+    def set_ctx(self, ctx):
+        """Reset the context of a node and all child nodes.  Per default the
+        parser will all generate nodes that have a 'load' context as it's the
+        most common one.  This method is used in the parser to set assignment
+        targets and other nodes to a store context.
+        """
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            if 'ctx' in node.fields:
+                node.ctx = ctx
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def set_lineno(self, lineno, override=False):
+        """Set the line numbers of the node and children."""
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            if 'lineno' in node.attributes:
+                if node.lineno is None or override:
+                    node.lineno = lineno
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def set_environment(self, environment):
+        """Set the environment for all nodes."""
+        todo = deque([self])
+        while todo:
+            node = todo.popleft()
+            node.environment = environment
+            todo.extend(node.iter_child_nodes())
+        return self
+
+    def __eq__(self, other):
+        return type(self) is type(other) and \
+               tuple(self.iter_fields()) == tuple(other.iter_fields())
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    # Restore Python 2 hashing behavior on Python 3
+    __hash__ = object.__hash__
+
+    def __repr__(self):
+        return '%s(%s)' % (
+            self.__class__.__name__,
+            ', '.join('%s=%r' % (arg, getattr(self, arg, None)) for
+                      arg in self.fields)
+        )
+
+    def dump(self):
+        def _dump(node):
+            if not isinstance(node, Node):
+                buf.append(repr(node))
+                return
+
+            buf.append('nodes.%s(' % node.__class__.__name__)
+            if not node.fields:
+                buf.append(')')
+                return
+            for idx, field in enumerate(node.fields):
+                if idx:
+                    buf.append(', ')
+                value = getattr(node, field)
+                if isinstance(value, list):
+                    buf.append('[')
+                    for idx, item in enumerate(value):
+                        if idx:
+                            buf.append(', ')
+                        _dump(item)
+                    buf.append(']')
+                else:
+                    _dump(value)
+            buf.append(')')
+        buf = []
+        _dump(self)
+        return ''.join(buf)
+
+
+
+class Stmt(Node):
+    """Base node for all statements."""
+    abstract = True
+
+
+class Helper(Node):
+    """Nodes that exist in a specific context only."""
+    abstract = True
+
+
+class Template(Node):
+    """Node that represents a template.  This must be the outermost node that
+    is passed to the compiler.
+    """
+    fields = ('body',)
+
+
+class Output(Stmt):
+    """A node that holds multiple expressions which are then printed out.
+    This is used both for the `print` statement and the regular template data.
+    """
+    fields = ('nodes',)
+
+
+class Extends(Stmt):
+    """Represents an extends statement."""
+    fields = ('template',)
+
+
+class For(Stmt):
+    """The for loop.  `target` is the target for the iteration (usually a
+    :class:`Name` or :class:`Tuple`), `iter` the iterable.  `body` is a list
+    of nodes that are used as loop-body, and `else_` a list of nodes for the
+    `else` block.  If no else node exists it has to be an empty list.
+
+    For filtered nodes an expression can be stored as `test`, otherwise `None`.
+    """
+    fields = ('target', 'iter', 'body', 'else_', 'test', 'recursive')
+
+
+class If(Stmt):
+    """If `test` is true, `body` is rendered, else `else_`."""
+    fields = ('test', 'body', 'elif_', 'else_')
+
+
+class Macro(Stmt):
+    """A macro definition.  `name` is the name of the macro, `args` a list of
+    arguments and `defaults` a list of defaults if there are any.  `body` is
+    a list of nodes for the macro body.
+    """
+    fields = ('name', 'args', 'defaults', 'body')
+
+
+class CallBlock(Stmt):
+    """Like a macro without a name but a call instead.  `call` is called with
+    the unnamed macro as `caller` argument this node holds.
+    """
+    fields = ('call', 'args', 'defaults', 'body')
+
+
+class FilterBlock(Stmt):
+    """Node for filter sections."""
+    fields = ('body', 'filter')
+
+
+class With(Stmt):
+    """Specific node for with statements.  In older versions of Jinja the
+    with statement was implemented on the base of the `Scope` node instead.
+
+    .. versionadded:: 2.9.3
+    """
+    fields = ('targets', 'values', 'body')
+
+
+class Block(Stmt):
+    """A node that represents a block."""
+    fields = ('name', 'body', 'scoped')
+
+
+class Include(Stmt):
+    """A node that represents the include tag."""
+    fields = ('template', 'with_context', 'ignore_missing')
+
+
+class Import(Stmt):
+    """A node that represents the import tag."""
+    fields = ('template', 'target', 'with_context')
+
+
+class FromImport(Stmt):
+    """A node that represents the from import tag.  It's important to not
+    pass unsafe names to the name attribute.  The compiler translates the
+    attribute lookups directly into getattr calls and does *not* use the
+    subscript callback of the interface.  As exported variables may not
+    start with double underscores (which the parser asserts) this is not a
+    problem for regular Jinja code, but if this node is used in an extension
+    extra care must be taken.
+
+    The list of names may contain tuples if aliases are wanted.
+    """
+    fields = ('template', 'names', 'with_context')
+
+
+class ExprStmt(Stmt):
+    """A statement that evaluates an expression and discards the result."""
+    fields = ('node',)
+
+
+class Assign(Stmt):
+    """Assigns an expression to a target."""
+    fields = ('target', 'node')
+
+
+class AssignBlock(Stmt):
+    """Assigns a block to a target."""
+    fields = ('target', 'filter', 'body')
+
+
+class Expr(Node):
+    """Baseclass for all expressions."""
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        """Return the value of the expression as constant or raise
+        :exc:`Impossible` if this was not possible.
+
+        An :class:`EvalContext` can be provided, if none is given
+        a default context is created which requires the nodes to have
+        an attached environment.
+
+        .. versionchanged:: 2.4
+           the `eval_ctx` parameter was added.
+        """
+        raise Impossible()
+
+    def can_assign(self):
+        """Check if it's possible to assign something to this node."""
+        return False
+
+
+class BinExpr(Expr):
+    """Baseclass for all binary expressions."""
+    fields = ('left', 'right')
+    operator = None
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        # intercepted operators cannot be folded at compile time
+        if self.environment.sandboxed and \
+           self.operator in self.environment.intercepted_binops:
+            raise Impossible()
+        f = _binop_to_func[self.operator]
+        try:
+            return f(self.left.as_const(eval_ctx), self.right.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+
+class UnaryExpr(Expr):
+    """Baseclass for all unary expressions."""
+    fields = ('node',)
+    operator = None
+    abstract = True
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        # intercepted operators cannot be folded at compile time
+        if self.environment.sandboxed and \
+           self.operator in self.environment.intercepted_unops:
+            raise Impossible()
+        f = _uaop_to_func[self.operator]
+        try:
+            return f(self.node.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+
+class Name(Expr):
+    """Looks up a name or stores a value in a name.
+    The `ctx` of the node can be one of the following values:
+
+    -   `store`: store a value in the name
+    -   `load`: load that name
+    -   `param`: like `store` but if the name was defined as function parameter.
+    """
+    fields = ('name', 'ctx')
+
+    def can_assign(self):
+        return self.name not in ('true', 'false', 'none',
+                                 'True', 'False', 'None')
+
+
+class NSRef(Expr):
+    """Reference to a namespace value assignment"""
+    fields = ('name', 'attr')
+
+    def can_assign(self):
+        # We don't need any special checks here; NSRef assignments have a
+        # runtime check to ensure the target is a namespace object which will
+        # have been checked already as it is created using a normal assignment
+        # which goes through a `Name` node.
+        return True
+
+
+class Literal(Expr):
+    """Baseclass for literals."""
+    abstract = True
+
+
+class Const(Literal):
+    """All constant values.  The parser will return this node for simple
+    constants such as ``42`` or ``"foo"`` but it can be used to store more
+    complex values such as lists too.  Only constants with a safe
+    representation (objects where ``eval(repr(x)) == x`` is true).
+    """
+    fields = ('value',)
+
+    def as_const(self, eval_ctx=None):
+        rv = self.value
+        if PY2 and type(rv) is text_type and \
+           self.environment.policies['compiler.ascii_str']:
+            try:
+                rv = rv.encode('ascii')
+            except UnicodeError:
+                pass
+        return rv
+
+    @classmethod
+    def from_untrusted(cls, value, lineno=None, environment=None):
+        """Return a const object if the value is representable as
+        constant value in the generated code, otherwise it will raise
+        an `Impossible` exception.
+        """
+        from .compiler import has_safe_repr
+        if not has_safe_repr(value):
+            raise Impossible()
+        return cls(value, lineno=lineno, environment=environment)
+
+
+class TemplateData(Literal):
+    """A constant template string."""
+    fields = ('data',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile:
+            raise Impossible()
+        if eval_ctx.autoescape:
+            return Markup(self.data)
+        return self.data
+
+
+class Tuple(Literal):
+    """For loop unpacking and some other things like multiple arguments
+    for subscripts.  Like for :class:`Name` `ctx` specifies if the tuple
+    is used for loading the names or storing.
+    """
+    fields = ('items', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return tuple(x.as_const(eval_ctx) for x in self.items)
+
+    def can_assign(self):
+        for item in self.items:
+            if not item.can_assign():
+                return False
+        return True
+
+
+class List(Literal):
+    """Any list literal such as ``[1, 2, 3]``"""
+    fields = ('items',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return [x.as_const(eval_ctx) for x in self.items]
+
+
+class Dict(Literal):
+    """Any dict literal such as ``{1: 2, 3: 4}``.  The items must be a list of
+    :class:`Pair` nodes.
+    """
+    fields = ('items',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return dict(x.as_const(eval_ctx) for x in self.items)
+
+
+class Pair(Helper):
+    """A key, value pair for dicts."""
+    fields = ('key', 'value')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.key.as_const(eval_ctx), self.value.as_const(eval_ctx)
+
+
+class Keyword(Helper):
+    """A key, value pair for keyword arguments where key is a string."""
+    fields = ('key', 'value')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.key, self.value.as_const(eval_ctx)
+
+
+class CondExpr(Expr):
+    """A conditional expression (inline if expression).  (``{{
+    foo if bar else baz }}``)
+    """
+    fields = ('test', 'expr1', 'expr2')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if self.test.as_const(eval_ctx):
+            return self.expr1.as_const(eval_ctx)
+
+        # if we evaluate to an undefined object, we better do that at runtime
+        if self.expr2 is None:
+            raise Impossible()
+
+        return self.expr2.as_const(eval_ctx)
+
+
+def args_as_const(node, eval_ctx):
+    args = [x.as_const(eval_ctx) for x in node.args]
+    kwargs = dict(x.as_const(eval_ctx) for x in node.kwargs)
+
+    if node.dyn_args is not None:
+        try:
+            args.extend(node.dyn_args.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+    if node.dyn_kwargs is not None:
+        try:
+            kwargs.update(node.dyn_kwargs.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+    return args, kwargs
+
+
+class Filter(Expr):
+    """This node applies a filter on an expression.  `name` is the name of
+    the filter, the rest of the fields are the same as for :class:`Call`.
+
+    If the `node` of a filter is `None` the contents of the last buffer are
+    filtered.  Buffers are created by macros and filter blocks.
+    """
+
+    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+
+        if eval_ctx.volatile or self.node is None:
+            raise Impossible()
+
+        # we have to be careful here because we call filter_ below.
+        # if this variable would be called filter, 2to3 would wrap the
+        # call in a list because it is assuming we are talking about the
+        # builtin filter function here which no longer returns a list in
+        # python 3.  because of that, do not rename filter_ to filter!
+        filter_ = self.environment.filters.get(self.name)
+
+        if filter_ is None or getattr(filter_, 'contextfilter', False):
+            raise Impossible()
+
+        # We cannot constant handle async filters, so we need to make sure
+        # to not go down this path.
+        if (
+            eval_ctx.environment.is_async
+            and getattr(filter_, 'asyncfiltervariant', False)
+        ):
+            raise Impossible()
+
+        args, kwargs = args_as_const(self, eval_ctx)
+        args.insert(0, self.node.as_const(eval_ctx))
+
+        if getattr(filter_, 'evalcontextfilter', False):
+            args.insert(0, eval_ctx)
+        elif getattr(filter_, 'environmentfilter', False):
+            args.insert(0, self.environment)
+
+        try:
+            return filter_(*args, **kwargs)
+        except Exception:
+            raise Impossible()
+
+
+class Test(Expr):
+    """Applies a test on an expression.  `name` is the name of the test, the
+    rest of the fields are the same as for :class:`Call`.
+    """
+
+    fields = ('node', 'name', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+    def as_const(self, eval_ctx=None):
+        test = self.environment.tests.get(self.name)
+
+        if test is None:
+            raise Impossible()
+
+        eval_ctx = get_eval_context(self, eval_ctx)
+        args, kwargs = args_as_const(self, eval_ctx)
+        args.insert(0, self.node.as_const(eval_ctx))
+
+        try:
+            return test(*args, **kwargs)
+        except Exception:
+            raise Impossible()
+
+
+class Call(Expr):
+    """Calls an expression.  `args` is a list of arguments, `kwargs` a list
+    of keyword arguments (list of :class:`Keyword` nodes), and `dyn_args`
+    and `dyn_kwargs` has to be either `None` or a node that is used as
+    node for dynamic positional (``*args``) or keyword (``**kwargs``)
+    arguments.
+    """
+    fields = ('node', 'args', 'kwargs', 'dyn_args', 'dyn_kwargs')
+
+
+class Getitem(Expr):
+    """Get an attribute or item from an expression and prefer the item."""
+    fields = ('node', 'arg', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if self.ctx != 'load':
+            raise Impossible()
+        try:
+            return self.environment.getitem(self.node.as_const(eval_ctx),
+                                            self.arg.as_const(eval_ctx))
+        except Exception:
+            raise Impossible()
+
+    def can_assign(self):
+        return False
+
+
+class Getattr(Expr):
+    """Get an attribute or item from an expression that is a ascii-only
+    bytestring and prefer the attribute.
+    """
+    fields = ('node', 'attr', 'ctx')
+
+    def as_const(self, eval_ctx=None):
+        if self.ctx != 'load':
+            raise Impossible()
+        try:
+            eval_ctx = get_eval_context(self, eval_ctx)
+            return self.environment.getattr(self.node.as_const(eval_ctx),
+                                            self.attr)
+        except Exception:
+            raise Impossible()
+
+    def can_assign(self):
+        return False
+
+
+class Slice(Expr):
+    """Represents a slice object.  This must only be used as argument for
+    :class:`Subscript`.
+    """
+    fields = ('start', 'stop', 'step')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        def const(obj):
+            if obj is None:
+                return None
+            return obj.as_const(eval_ctx)
+        return slice(const(self.start), const(self.stop), const(self.step))
+
+
+class Concat(Expr):
+    """Concatenates the list of expressions provided after converting them to
+    unicode.
+    """
+    fields = ('nodes',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return ''.join(text_type(x.as_const(eval_ctx)) for x in self.nodes)
+
+
+class Compare(Expr):
+    """Compares an expression with some other expressions.  `ops` must be a
+    list of :class:`Operand`\\s.
+    """
+    fields = ('expr', 'ops')
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        result = value = self.expr.as_const(eval_ctx)
+
+        try:
+            for op in self.ops:
+                new_value = op.expr.as_const(eval_ctx)
+                result = _cmpop_to_func[op.op](value, new_value)
+
+                if not result:
+                    return False
+
+                value = new_value
+        except Exception:
+            raise Impossible()
+
+        return result
+
+
+class Operand(Helper):
+    """Holds an operator and an expression."""
+    fields = ('op', 'expr')
+
+if __debug__:
+    Operand.__doc__ += '\nThe following operators are available: ' + \
+        ', '.join(sorted('``%s``' % x for x in set(_binop_to_func) |
+                  set(_uaop_to_func) | set(_cmpop_to_func)))
+
+
+class Mul(BinExpr):
+    """Multiplies the left with the right node."""
+    operator = '*'
+
+
+class Div(BinExpr):
+    """Divides the left by the right node."""
+    operator = '/'
+
+
+class FloorDiv(BinExpr):
+    """Divides the left by the right node and truncates conver the
+    result into an integer by truncating.
+    """
+    operator = '//'
+
+
+class Add(BinExpr):
+    """Add the left to the right node."""
+    operator = '+'
+
+
+class Sub(BinExpr):
+    """Subtract the right from the left node."""
+    operator = '-'
+
+
+class Mod(BinExpr):
+    """Left modulo right."""
+    operator = '%'
+
+
+class Pow(BinExpr):
+    """Left to the power of right."""
+    operator = '**'
+
+
+class And(BinExpr):
+    """Short circuited AND."""
+    operator = 'and'
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.left.as_const(eval_ctx) and self.right.as_const(eval_ctx)
+
+
+class Or(BinExpr):
+    """Short circuited OR."""
+    operator = 'or'
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return self.left.as_const(eval_ctx) or self.right.as_const(eval_ctx)
+
+
+class Not(UnaryExpr):
+    """Negate the expression."""
+    operator = 'not'
+
+
+class Neg(UnaryExpr):
+    """Make the expression negative."""
+    operator = '-'
+
+
+class Pos(UnaryExpr):
+    """Make the expression positive (noop for most expressions)"""
+    operator = '+'
+
+
+# Helpers for extensions
+
+
+class EnvironmentAttribute(Expr):
+    """Loads an attribute from the environment object.  This is useful for
+    extensions that want to call a callback stored on the environment.
+    """
+    fields = ('name',)
+
+
+class ExtensionAttribute(Expr):
+    """Returns the attribute of an extension bound to the environment.
+    The identifier is the identifier of the :class:`Extension`.
+
+    This node is usually constructed by calling the
+    :meth:`~jinja2.ext.Extension.attr` method on an extension.
+    """
+    fields = ('identifier', 'name')
+
+
+class ImportedName(Expr):
+    """If created with an import name the import name is returned on node
+    access.  For example ``ImportedName('cgi.escape')`` returns the `escape`
+    function from the cgi module on evaluation.  Imports are optimized by the
+    compiler so there is no need to assign them to local variables.
+    """
+    fields = ('importname',)
+
+
+class InternalName(Expr):
+    """An internal name in the compiler.  You cannot create these nodes
+    yourself but the parser provides a
+    :meth:`~jinja2.parser.Parser.free_identifier` method that creates
+    a new identifier for you.  This identifier is not available from the
+    template and is not threated specially by the compiler.
+    """
+    fields = ('name',)
+
+    def __init__(self):
+        raise TypeError('Can\'t create internal names.  Use the '
+                        '`free_identifier` method on a parser.')
+
+
+class MarkSafe(Expr):
+    """Mark the wrapped expression as safe (wrap it as `Markup`)."""
+    fields = ('expr',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        return Markup(self.expr.as_const(eval_ctx))
+
+
+class MarkSafeIfAutoescape(Expr):
+    """Mark the wrapped expression as safe (wrap it as `Markup`) but
+    only if autoescaping is active.
+
+    .. versionadded:: 2.5
+    """
+    fields = ('expr',)
+
+    def as_const(self, eval_ctx=None):
+        eval_ctx = get_eval_context(self, eval_ctx)
+        if eval_ctx.volatile:
+            raise Impossible()
+        expr = self.expr.as_const(eval_ctx)
+        if eval_ctx.autoescape:
+            return Markup(expr)
+        return expr
+
+
+class ContextReference(Expr):
+    """Returns the current template context.  It can be used like a
+    :class:`Name` node, with a ``'load'`` ctx and will return the
+    current :class:`~jinja2.runtime.Context` object.
+
+    Here an example that assigns the current template name to a
+    variable named `foo`::
+
+        Assign(Name('foo', ctx='store'),
+               Getattr(ContextReference(), 'name'))
+
+    This is basically equivalent to using the
+    :func:`~jinja2.contextfunction` decorator when using the
+    high-level API, which causes a reference to the context to be passed
+    as the first argument to a function.
+    """
+
+
+class DerivedContextReference(Expr):
+    """Return the current template context including locals. Behaves
+    exactly like :class:`ContextReference`, but includes local
+    variables, such as from a ``for`` loop.
+
+    .. versionadded:: 2.11
+    """
+
+
+class Continue(Stmt):
+    """Continue a loop."""
+
+
+class Break(Stmt):
+    """Break a loop."""
+
+
+class Scope(Stmt):
+    """An artificial scope."""
+    fields = ('body',)
+
+
+class OverlayScope(Stmt):
+    """An overlay scope for extensions.  This is a largely unoptimized scope
+    that however can be used to introduce completely arbitrary variables into
+    a sub scope from a dictionary or dictionary like object.  The `context`
+    field has to evaluate to a dictionary object.
+
+    Example usage::
+
+        OverlayScope(context=self.call_method('get_context'),
+                     body=[...])
+
+    .. versionadded:: 2.10
+    """
+    fields = ('context', 'body')
+
+
+class EvalContextModifier(Stmt):
+    """Modifies the eval context.  For each option that should be modified,
+    a :class:`Keyword` has to be added to the :attr:`options` list.
+
+    Example to change the `autoescape` setting::
+
+        EvalContextModifier(options=[Keyword('autoescape', Const(True))])
+    """
+    fields = ('options',)
+
+
+class ScopedEvalContextModifier(EvalContextModifier):
+    """Modifies the eval context and reverts it later.  Works exactly like
+    :class:`EvalContextModifier` but will only modify the
+    :class:`~jinja2.nodes.EvalContext` for nodes in the :attr:`body`.
+    """
+    fields = ('body',)
+
+
+# make sure nobody creates custom nodes
+def _failing_new(*args, **kwargs):
+    raise TypeError('can\'t create custom node types')
+NodeType.__new__ = staticmethod(_failing_new); del _failing_new
diff --git a/src/jinja2/optimizer.py b/src/jinja2/optimizer.py
new file mode 100644
index 0000000..7065424
--- /dev/null
+++ b/src/jinja2/optimizer.py
@@ -0,0 +1,49 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.optimizer
+    ~~~~~~~~~~~~~~~~
+
+    The jinja optimizer is currently trying to constant fold a few expressions
+    and modify the AST in place so that it should be easier to evaluate it.
+
+    Because the AST does not contain all the scoping information and the
+    compiler has to find that out, we cannot do all the optimizations we
+    want.  For example loop unrolling doesn't work because unrolled loops would
+    have a different scoping.
+
+    The solution would be a second syntax tree that has the scoping rules stored.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+from jinja2 import nodes
+from jinja2.visitor import NodeTransformer
+
+
+def optimize(node, environment):
+    """The context hint can be used to perform an static optimization
+    based on the context given."""
+    optimizer = Optimizer(environment)
+    return optimizer.visit(node)
+
+
+class Optimizer(NodeTransformer):
+    def __init__(self, environment):
+        self.environment = environment
+
+    def generic_visit(self, node, *args, **kwargs):
+        node = super(Optimizer, self).generic_visit(node, *args, **kwargs)
+
+        # Do constant folding. Some other nodes besides Expr have
+        # as_const, but folding them causes errors later on.
+        if isinstance(node, nodes.Expr):
+            try:
+                return nodes.Const.from_untrusted(
+                    node.as_const(args[0] if args else None),
+                    lineno=node.lineno,
+                    environment=self.environment,
+                )
+            except nodes.Impossible:
+                pass
+
+        return node
diff --git a/src/jinja2/parser.py b/src/jinja2/parser.py
new file mode 100644
index 0000000..7403b08
--- /dev/null
+++ b/src/jinja2/parser.py
@@ -0,0 +1,907 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.parser
+    ~~~~~~~~~~~~~
+
+    Implements the template parser.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+from jinja2 import nodes
+from jinja2.exceptions import TemplateSyntaxError, TemplateAssertionError
+from jinja2.lexer import describe_token, describe_token_expr
+from jinja2._compat import imap
+
+
+_statement_keywords = frozenset(['for', 'if', 'block', 'extends', 'print',
+                                 'macro', 'include', 'from', 'import',
+                                 'set', 'with', 'autoescape'])
+_compare_operators = frozenset(['eq', 'ne', 'lt', 'lteq', 'gt', 'gteq'])
+
+_math_nodes = {
+    'add': nodes.Add,
+    'sub': nodes.Sub,
+    'mul': nodes.Mul,
+    'div': nodes.Div,
+    'floordiv': nodes.FloorDiv,
+    'mod': nodes.Mod,
+}
+
+
+class Parser(object):
+    """This is the central parsing class Jinja uses.  It's passed to
+    extensions and can be used to parse expressions or statements.
+    """
+
+    def __init__(self, environment, source, name=None, filename=None,
+                 state=None):
+        self.environment = environment
+        self.stream = environment._tokenize(source, name, filename, state)
+        self.name = name
+        self.filename = filename
+        self.closed = False
+        self.extensions = {}
+        for extension in environment.iter_extensions():
+            for tag in extension.tags:
+                self.extensions[tag] = extension.parse
+        self._last_identifier = 0
+        self._tag_stack = []
+        self._end_token_stack = []
+
+    def fail(self, msg, lineno=None, exc=TemplateSyntaxError):
+        """Convenience method that raises `exc` with the message, passed
+        line number or last line number as well as the current name and
+        filename.
+        """
+        if lineno is None:
+            lineno = self.stream.current.lineno
+        raise exc(msg, lineno, self.name, self.filename)
+
+    def _fail_ut_eof(self, name, end_token_stack, lineno):
+        expected = []
+        for exprs in end_token_stack:
+            expected.extend(imap(describe_token_expr, exprs))
+        if end_token_stack:
+            currently_looking = ' or '.join(
+                "'%s'" % describe_token_expr(expr)
+                for expr in end_token_stack[-1])
+        else:
+            currently_looking = None
+
+        if name is None:
+            message = ['Unexpected end of template.']
+        else:
+            message = ['Encountered unknown tag \'%s\'.' % name]
+
+        if currently_looking:
+            if name is not None and name in expected:
+                message.append('You probably made a nesting mistake. Jinja '
+                               'is expecting this tag, but currently looking '
+                               'for %s.' % currently_looking)
+            else:
+                message.append('Jinja was looking for the following tags: '
+                               '%s.' % currently_looking)
+
+        if self._tag_stack:
+            message.append('The innermost block that needs to be '
+                           'closed is \'%s\'.' % self._tag_stack[-1])
+
+        self.fail(' '.join(message), lineno)
+
+    def fail_unknown_tag(self, name, lineno=None):
+        """Called if the parser encounters an unknown tag.  Tries to fail
+        with a human readable error message that could help to identify
+        the problem.
+        """
+        return self._fail_ut_eof(name, self._end_token_stack, lineno)
+
+    def fail_eof(self, end_tokens=None, lineno=None):
+        """Like fail_unknown_tag but for end of template situations."""
+        stack = list(self._end_token_stack)
+        if end_tokens is not None:
+            stack.append(end_tokens)
+        return self._fail_ut_eof(None, stack, lineno)
+
+    def is_tuple_end(self, extra_end_rules=None):
+        """Are we at the end of a tuple?"""
+        if self.stream.current.type in ('variable_end', 'block_end', 'rparen'):
+            return True
+        elif extra_end_rules is not None:
+            return self.stream.current.test_any(extra_end_rules)
+        return False
+
+    def free_identifier(self, lineno=None):
+        """Return a new free identifier as :class:`~jinja2.nodes.InternalName`."""
+        self._last_identifier += 1
+        rv = object.__new__(nodes.InternalName)
+        nodes.Node.__init__(rv, 'fi%d' % self._last_identifier, lineno=lineno)
+        return rv
+
+    def parse_statement(self):
+        """Parse a single statement."""
+        token = self.stream.current
+        if token.type != 'name':
+            self.fail('tag name expected', token.lineno)
+        self._tag_stack.append(token.value)
+        pop_tag = True
+        try:
+            if token.value in _statement_keywords:
+                return getattr(self, 'parse_' + self.stream.current.value)()
+            if token.value == 'call':
+                return self.parse_call_block()
+            if token.value == 'filter':
+                return self.parse_filter_block()
+            ext = self.extensions.get(token.value)
+            if ext is not None:
+                return ext(self)
+
+            # did not work out, remove the token we pushed by accident
+            # from the stack so that the unknown tag fail function can
+            # produce a proper error message.
+            self._tag_stack.pop()
+            pop_tag = False
+            self.fail_unknown_tag(token.value, token.lineno)
+        finally:
+            if pop_tag:
+                self._tag_stack.pop()
+
+    def parse_statements(self, end_tokens, drop_needle=False):
+        """Parse multiple statements into a list until one of the end tokens
+        is reached.  This is used to parse the body of statements as it also
+        parses template data if appropriate.  The parser checks first if the
+        current token is a colon and skips it if there is one.  Then it checks
+        for the block end and parses until if one of the `end_tokens` is
+        reached.  Per default the active token in the stream at the end of
+        the call is the matched end token.  If this is not wanted `drop_needle`
+        can be set to `True` and the end token is removed.
+        """
+        # the first token may be a colon for python compatibility
+        self.stream.skip_if('colon')
+
+        # in the future it would be possible to add whole code sections
+        # by adding some sort of end of statement token and parsing those here.
+        self.stream.expect('block_end')
+        result = self.subparse(end_tokens)
+
+        # we reached the end of the template too early, the subparser
+        # does not check for this, so we do that now
+        if self.stream.current.type == 'eof':
+            self.fail_eof(end_tokens)
+
+        if drop_needle:
+            next(self.stream)
+        return result
+
+    def parse_set(self):
+        """Parse an assign statement."""
+        lineno = next(self.stream).lineno
+        target = self.parse_assign_target(with_namespace=True)
+        if self.stream.skip_if('assign'):
+            expr = self.parse_tuple()
+            return nodes.Assign(target, expr, lineno=lineno)
+        filter_node = self.parse_filter(None)
+        body = self.parse_statements(('name:endset',),
+                                     drop_needle=True)
+        return nodes.AssignBlock(target, filter_node, body, lineno=lineno)
+
+    def parse_for(self):
+        """Parse a for loop."""
+        lineno = self.stream.expect('name:for').lineno
+        target = self.parse_assign_target(extra_end_rules=('name:in',))
+        self.stream.expect('name:in')
+        iter = self.parse_tuple(with_condexpr=False,
+                                extra_end_rules=('name:recursive',))
+        test = None
+        if self.stream.skip_if('name:if'):
+            test = self.parse_expression()
+        recursive = self.stream.skip_if('name:recursive')
+        body = self.parse_statements(('name:endfor', 'name:else'))
+        if next(self.stream).value == 'endfor':
+            else_ = []
+        else:
+            else_ = self.parse_statements(('name:endfor',), drop_needle=True)
+        return nodes.For(target, iter, body, else_, test,
+                         recursive, lineno=lineno)
+
+    def parse_if(self):
+        """Parse an if construct."""
+        node = result = nodes.If(lineno=self.stream.expect('name:if').lineno)
+        while 1:
+            node.test = self.parse_tuple(with_condexpr=False)
+            node.body = self.parse_statements(('name:elif', 'name:else',
+                                               'name:endif'))
+            node.elif_ = []
+            node.else_ = []
+            token = next(self.stream)
+            if token.test('name:elif'):
+                node = nodes.If(lineno=self.stream.current.lineno)
+                result.elif_.append(node)
+                continue
+            elif token.test('name:else'):
+                result.else_ = self.parse_statements(('name:endif',),
+                                                     drop_needle=True)
+            break
+        return result
+
+    def parse_with(self):
+        node = nodes.With(lineno=next(self.stream).lineno)
+        targets = []
+        values = []
+        while self.stream.current.type != 'block_end':
+            lineno = self.stream.current.lineno
+            if targets:
+                self.stream.expect('comma')
+            target = self.parse_assign_target()
+            target.set_ctx('param')
+            targets.append(target)
+            self.stream.expect('assign')
+            values.append(self.parse_expression())
+        node.targets = targets
+        node.values = values
+        node.body = self.parse_statements(('name:endwith',),
+                                          drop_needle=True)
+        return node
+
+    def parse_autoescape(self):
+        node = nodes.ScopedEvalContextModifier(lineno=next(self.stream).lineno)
+        node.options = [
+            nodes.Keyword('autoescape', self.parse_expression())
+        ]
+        node.body = self.parse_statements(('name:endautoescape',),
+                                            drop_needle=True)
+        return nodes.Scope([node])
+
+    def parse_block(self):
+        node = nodes.Block(lineno=next(self.stream).lineno)
+        node.name = self.stream.expect('name').value
+        node.scoped = self.stream.skip_if('name:scoped')
+
+        # common problem people encounter when switching from django
+        # to jinja.  we do not support hyphens in block names, so let's
+        # raise a nicer error message in that case.
+        if self.stream.current.type == 'sub':
+            self.fail('Block names in Jinja have to be valid Python '
+                      'identifiers and may not contain hyphens, use an '
+                      'underscore instead.')
+
+        node.body = self.parse_statements(('name:endblock',), drop_needle=True)
+        self.stream.skip_if('name:' + node.name)
+        return node
+
+    def parse_extends(self):
+        node = nodes.Extends(lineno=next(self.stream).lineno)
+        node.template = self.parse_expression()
+        return node
+
+    def parse_import_context(self, node, default):
+        if self.stream.current.test_any('name:with', 'name:without') and \
+           self.stream.look().test('name:context'):
+            node.with_context = next(self.stream).value == 'with'
+            self.stream.skip()
+        else:
+            node.with_context = default
+        return node
+
+    def parse_include(self):
+        node = nodes.Include(lineno=next(self.stream).lineno)
+        node.template = self.parse_expression()
+        if self.stream.current.test('name:ignore') and \
+           self.stream.look().test('name:missing'):
+            node.ignore_missing = True
+            self.stream.skip(2)
+        else:
+            node.ignore_missing = False
+        return self.parse_import_context(node, True)
+
+    def parse_import(self):
+        node = nodes.Import(lineno=next(self.stream).lineno)
+        node.template = self.parse_expression()
+        self.stream.expect('name:as')
+        node.target = self.parse_assign_target(name_only=True).name
+        return self.parse_import_context(node, False)
+
+    def parse_from(self):
+        node = nodes.FromImport(lineno=next(self.stream).lineno)
+        node.template = self.parse_expression()
+        self.stream.expect('name:import')
+        node.names = []
+
+        def parse_context():
+            if self.stream.current.value in ('with', 'without') and \
+               self.stream.look().test('name:context'):
+                node.with_context = next(self.stream).value == 'with'
+                self.stream.skip()
+                return True
+            return False
+
+        while 1:
+            if node.names:
+                self.stream.expect('comma')
+            if self.stream.current.type == 'name':
+                if parse_context():
+                    break
+                target = self.parse_assign_target(name_only=True)
+                if target.name.startswith('_'):
+                    self.fail('names starting with an underline can not '
+                              'be imported', target.lineno,
+                              exc=TemplateAssertionError)
+                if self.stream.skip_if('name:as'):
+                    alias = self.parse_assign_target(name_only=True)
+                    node.names.append((target.name, alias.name))
+                else:
+                    node.names.append(target.name)
+                if parse_context() or self.stream.current.type != 'comma':
+                    break
+            else:
+                self.stream.expect('name')
+        if not hasattr(node, 'with_context'):
+            node.with_context = False
+        return node
+
+    def parse_signature(self, node):
+        node.args = args = []
+        node.defaults = defaults = []
+        self.stream.expect('lparen')
+        while self.stream.current.type != 'rparen':
+            if args:
+                self.stream.expect('comma')
+            arg = self.parse_assign_target(name_only=True)
+            arg.set_ctx('param')
+            if self.stream.skip_if('assign'):
+                defaults.append(self.parse_expression())
+            elif defaults:
+                self.fail('non-default argument follows default argument')
+            args.append(arg)
+        self.stream.expect('rparen')
+
+    def parse_call_block(self):
+        node = nodes.CallBlock(lineno=next(self.stream).lineno)
+        if self.stream.current.type == 'lparen':
+            self.parse_signature(node)
+        else:
+            node.args = []
+            node.defaults = []
+
+        node.call = self.parse_expression()
+        if not isinstance(node.call, nodes.Call):
+            self.fail('expected call', node.lineno)
+        node.body = self.parse_statements(('name:endcall',), drop_needle=True)
+        return node
+
+    def parse_filter_block(self):
+        node = nodes.FilterBlock(lineno=next(self.stream).lineno)
+        node.filter = self.parse_filter(None, start_inline=True)
+        node.body = self.parse_statements(('name:endfilter',),
+                                          drop_needle=True)
+        return node
+
+    def parse_macro(self):
+        node = nodes.Macro(lineno=next(self.stream).lineno)
+        node.name = self.parse_assign_target(name_only=True).name
+        self.parse_signature(node)
+        node.body = self.parse_statements(('name:endmacro',),
+                                          drop_needle=True)
+        return node
+
+    def parse_print(self):
+        node = nodes.Output(lineno=next(self.stream).lineno)
+        node.nodes = []
+        while self.stream.current.type != 'block_end':
+            if node.nodes:
+                self.stream.expect('comma')
+            node.nodes.append(self.parse_expression())
+        return node
+
+    def parse_assign_target(self, with_tuple=True, name_only=False,
+                            extra_end_rules=None, with_namespace=False):
+        """Parse an assignment target.  As Jinja allows assignments to
+        tuples, this function can parse all allowed assignment targets.  Per
+        default assignments to tuples are parsed, that can be disable however
+        by setting `with_tuple` to `False`.  If only assignments to names are
+        wanted `name_only` can be set to `True`.  The `extra_end_rules`
+        parameter is forwarded to the tuple parsing function.  If
+        `with_namespace` is enabled, a namespace assignment may be parsed.
+        """
+        if with_namespace and self.stream.look().type == 'dot':
+            token = self.stream.expect('name')
+            next(self.stream)  # dot
+            attr = self.stream.expect('name')
+            target = nodes.NSRef(token.value, attr.value, lineno=token.lineno)
+        elif name_only:
+            token = self.stream.expect('name')
+            target = nodes.Name(token.value, 'store', lineno=token.lineno)
+        else:
+            if with_tuple:
+                target = self.parse_tuple(simplified=True,
+                                          extra_end_rules=extra_end_rules)
+            else:
+                target = self.parse_primary()
+            target.set_ctx('store')
+        if not target.can_assign():
+            self.fail('can\'t assign to %r' % target.__class__.
+                      __name__.lower(), target.lineno)
+        return target
+
+    def parse_expression(self, with_condexpr=True):
+        """Parse an expression.  Per default all expressions are parsed, if
+        the optional `with_condexpr` parameter is set to `False` conditional
+        expressions are not parsed.
+        """
+        if with_condexpr:
+            return self.parse_condexpr()
+        return self.parse_or()
+
+    def parse_condexpr(self):
+        lineno = self.stream.current.lineno
+        expr1 = self.parse_or()
+        while self.stream.skip_if('name:if'):
+            expr2 = self.parse_or()
+            if self.stream.skip_if('name:else'):
+                expr3 = self.parse_condexpr()
+            else:
+                expr3 = None
+            expr1 = nodes.CondExpr(expr2, expr1, expr3, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return expr1
+
+    def parse_or(self):
+        lineno = self.stream.current.lineno
+        left = self.parse_and()
+        while self.stream.skip_if('name:or'):
+            right = self.parse_and()
+            left = nodes.Or(left, right, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return left
+
+    def parse_and(self):
+        lineno = self.stream.current.lineno
+        left = self.parse_not()
+        while self.stream.skip_if('name:and'):
+            right = self.parse_not()
+            left = nodes.And(left, right, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return left
+
+    def parse_not(self):
+        if self.stream.current.test('name:not'):
+            lineno = next(self.stream).lineno
+            return nodes.Not(self.parse_not(), lineno=lineno)
+        return self.parse_compare()
+
+    def parse_compare(self):
+        lineno = self.stream.current.lineno
+        expr = self.parse_math1()
+        ops = []
+        while 1:
+            token_type = self.stream.current.type
+            if token_type in _compare_operators:
+                next(self.stream)
+                ops.append(nodes.Operand(token_type, self.parse_math1()))
+            elif self.stream.skip_if('name:in'):
+                ops.append(nodes.Operand('in', self.parse_math1()))
+            elif (self.stream.current.test('name:not') and
+                  self.stream.look().test('name:in')):
+                self.stream.skip(2)
+                ops.append(nodes.Operand('notin', self.parse_math1()))
+            else:
+                break
+            lineno = self.stream.current.lineno
+        if not ops:
+            return expr
+        return nodes.Compare(expr, ops, lineno=lineno)
+
+    def parse_math1(self):
+        lineno = self.stream.current.lineno
+        left = self.parse_concat()
+        while self.stream.current.type in ('add', 'sub'):
+            cls = _math_nodes[self.stream.current.type]
+            next(self.stream)
+            right = self.parse_concat()
+            left = cls(left, right, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return left
+
+    def parse_concat(self):
+        lineno = self.stream.current.lineno
+        args = [self.parse_math2()]
+        while self.stream.current.type == 'tilde':
+            next(self.stream)
+            args.append(self.parse_math2())
+        if len(args) == 1:
+            return args[0]
+        return nodes.Concat(args, lineno=lineno)
+
+    def parse_math2(self):
+        lineno = self.stream.current.lineno
+        left = self.parse_pow()
+        while self.stream.current.type in ('mul', 'div', 'floordiv', 'mod'):
+            cls = _math_nodes[self.stream.current.type]
+            next(self.stream)
+            right = self.parse_pow()
+            left = cls(left, right, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return left
+
+    def parse_pow(self):
+        lineno = self.stream.current.lineno
+        left = self.parse_unary()
+        while self.stream.current.type == 'pow':
+            next(self.stream)
+            right = self.parse_unary()
+            left = nodes.Pow(left, right, lineno=lineno)
+            lineno = self.stream.current.lineno
+        return left
+
+    def parse_unary(self, with_filter=True):
+        token_type = self.stream.current.type
+        lineno = self.stream.current.lineno
+        if token_type == 'sub':
+            next(self.stream)
+            node = nodes.Neg(self.parse_unary(False), lineno=lineno)
+        elif token_type == 'add':
+            next(self.stream)
+            node = nodes.Pos(self.parse_unary(False), lineno=lineno)
+        else:
+            node = self.parse_primary()
+        node = self.parse_postfix(node)
+        if with_filter:
+            node = self.parse_filter_expr(node)
+        return node
+
+    def parse_primary(self):
+        token = self.stream.current
+        if token.type == 'name':
+            if token.value in ('true', 'false', 'True', 'False'):
+                node = nodes.Const(token.value in ('true', 'True'),
+                                   lineno=token.lineno)
+            elif token.value in ('none', 'None'):
+                node = nodes.Const(None, lineno=token.lineno)
+            else:
+                node = nodes.Name(token.value, 'load', lineno=token.lineno)
+            next(self.stream)
+        elif token.type == 'string':
+            next(self.stream)
+            buf = [token.value]
+            lineno = token.lineno
+            while self.stream.current.type == 'string':
+                buf.append(self.stream.current.value)
+                next(self.stream)
+            node = nodes.Const(''.join(buf), lineno=lineno)
+        elif token.type in ('integer', 'float'):
+            next(self.stream)
+            node = nodes.Const(token.value, lineno=token.lineno)
+        elif token.type == 'lparen':
+            next(self.stream)
+            node = self.parse_tuple(explicit_parentheses=True)
+            self.stream.expect('rparen')
+        elif token.type == 'lbracket':
+            node = self.parse_list()
+        elif token.type == 'lbrace':
+            node = self.parse_dict()
+        else:
+            self.fail("unexpected '%s'" % describe_token(token), token.lineno)
+        return node
+
+    def parse_tuple(self, simplified=False, with_condexpr=True,
+                    extra_end_rules=None, explicit_parentheses=False):
+        """Works like `parse_expression` but if multiple expressions are
+        delimited by a comma a :class:`~jinja2.nodes.Tuple` node is created.
+        This method could also return a regular expression instead of a tuple
+        if no commas where found.
+
+        The default parsing mode is a full tuple.  If `simplified` is `True`
+        only names and literals are parsed.  The `no_condexpr` parameter is
+        forwarded to :meth:`parse_expression`.
+
+        Because tuples do not require delimiters and may end in a bogus comma
+        an extra hint is needed that marks the end of a tuple.  For example
+        for loops support tuples between `for` and `in`.  In that case the
+        `extra_end_rules` is set to ``['name:in']``.
+
+        `explicit_parentheses` is true if the parsing was triggered by an
+        expression in parentheses.  This is used to figure out if an empty
+        tuple is a valid expression or not.
+        """
+        lineno = self.stream.current.lineno
+        if simplified:
+            parse = self.parse_primary
+        elif with_condexpr:
+            parse = self.parse_expression
+        else:
+            parse = lambda: self.parse_expression(with_condexpr=False)
+        args = []
+        is_tuple = False
+        while 1:
+            if args:
+                self.stream.expect('comma')
+            if self.is_tuple_end(extra_end_rules):
+                break
+            args.append(parse())
+            if self.stream.current.type == 'comma':
+                is_tuple = True
+            else:
+                break
+            lineno = self.stream.current.lineno
+
+        if not is_tuple:
+            if args:
+                return args[0]
+
+            # if we don't have explicit parentheses, an empty tuple is
+            # not a valid expression.  This would mean nothing (literally
+            # nothing) in the spot of an expression would be an empty
+            # tuple.
+            if not explicit_parentheses:
+                self.fail('Expected an expression, got \'%s\'' %
+                          describe_token(self.stream.current))
+
+        return nodes.Tuple(args, 'load', lineno=lineno)
+
+    def parse_list(self):
+        token = self.stream.expect('lbracket')
+        items = []
+        while self.stream.current.type != 'rbracket':
+            if items:
+                self.stream.expect('comma')
+            if self.stream.current.type == 'rbracket':
+                break
+            items.append(self.parse_expression())
+        self.stream.expect('rbracket')
+        return nodes.List(items, lineno=token.lineno)
+
+    def parse_dict(self):
+        token = self.stream.expect('lbrace')
+        items = []
+        while self.stream.current.type != 'rbrace':
+            if items:
+                self.stream.expect('comma')
+            if self.stream.current.type == 'rbrace':
+                break
+            key = self.parse_expression()
+            self.stream.expect('colon')
+            value = self.parse_expression()
+            items.append(nodes.Pair(key, value, lineno=key.lineno))
+        self.stream.expect('rbrace')
+        return nodes.Dict(items, lineno=token.lineno)
+
+    def parse_postfix(self, node):
+        while 1:
+            token_type = self.stream.current.type
+            if token_type == 'dot' or token_type == 'lbracket':
+                node = self.parse_subscript(node)
+            # calls are valid both after postfix expressions (getattr
+            # and getitem) as well as filters and tests
+            elif token_type == 'lparen':
+                node = self.parse_call(node)
+            else:
+                break
+        return node
+
+    def parse_filter_expr(self, node):
+        while 1:
+            token_type = self.stream.current.type
+            if token_type == 'pipe':
+                node = self.parse_filter(node)
+            elif token_type == 'name' and self.stream.current.value == 'is':
+                node = self.parse_test(node)
+            # calls are valid both after postfix expressions (getattr
+            # and getitem) as well as filters and tests
+            elif token_type == 'lparen':
+                node = self.parse_call(node)
+            else:
+                break
+        return node
+
+    def parse_subscript(self, node):
+        token = next(self.stream)
+        if token.type == 'dot':
+            attr_token = self.stream.current
+            next(self.stream)
+            if attr_token.type == 'name':
+                return nodes.Getattr(node, attr_token.value, 'load',
+                                     lineno=token.lineno)
+            elif attr_token.type != 'integer':
+                self.fail('expected name or number', attr_token.lineno)
+            arg = nodes.Const(attr_token.value, lineno=attr_token.lineno)
+            return nodes.Getitem(node, arg, 'load', lineno=token.lineno)
+        if token.type == 'lbracket':
+            args = []
+            while self.stream.current.type != 'rbracket':
+                if args:
+                    self.stream.expect('comma')
+                args.append(self.parse_subscribed())
+            self.stream.expect('rbracket')
+            if len(args) == 1:
+                arg = args[0]
+            else:
+                arg = nodes.Tuple(args, 'load', lineno=token.lineno)
+            return nodes.Getitem(node, arg, 'load', lineno=token.lineno)
+        self.fail('expected subscript expression', token.lineno)
+
+    def parse_subscribed(self):
+        lineno = self.stream.current.lineno
+
+        if self.stream.current.type == 'colon':
+            next(self.stream)
+            args = [None]
+        else:
+            node = self.parse_expression()
+            if self.stream.current.type != 'colon':
+                return node
+            next(self.stream)
+            args = [node]
+
+        if self.stream.current.type == 'colon':
+            args.append(None)
+        elif self.stream.current.type not in ('rbracket', 'comma'):
+            args.append(self.parse_expression())
+        else:
+            args.append(None)
+
+        if self.stream.current.type == 'colon':
+            next(self.stream)
+            if self.stream.current.type not in ('rbracket', 'comma'):
+                args.append(self.parse_expression())
+            else:
+                args.append(None)
+        else:
+            args.append(None)
+
+        return nodes.Slice(lineno=lineno, *args)
+
+    def parse_call(self, node):
+        token = self.stream.expect('lparen')
+        args = []
+        kwargs = []
+        dyn_args = dyn_kwargs = None
+        require_comma = False
+
+        def ensure(expr):
+            if not expr:
+                self.fail('invalid syntax for function call expression',
+                          token.lineno)
+
+        while self.stream.current.type != 'rparen':
+            if require_comma:
+                self.stream.expect('comma')
+                # support for trailing comma
+                if self.stream.current.type == 'rparen':
+                    break
+            if self.stream.current.type == 'mul':
+                ensure(dyn_args is None and dyn_kwargs is None)
+                next(self.stream)
+                dyn_args = self.parse_expression()
+            elif self.stream.current.type == 'pow':
+                ensure(dyn_kwargs is None)
+                next(self.stream)
+                dyn_kwargs = self.parse_expression()
+            else:
+                if self.stream.current.type == 'name' and \
+                   self.stream.look().type == 'assign':
+                    # Parsing a kwarg
+                    ensure(dyn_kwargs is None)
+                    key = self.stream.current.value
+                    self.stream.skip(2)
+                    value = self.parse_expression()
+                    kwargs.append(nodes.Keyword(key, value,
+                                                lineno=value.lineno))
+                else:
+                    # Parsing an arg
+                    ensure(dyn_args is None and dyn_kwargs is None and not kwargs)
+                    args.append(self.parse_expression())
+
+            require_comma = True
+        self.stream.expect('rparen')
+
+        if node is None:
+            return args, kwargs, dyn_args, dyn_kwargs
+        return nodes.Call(node, args, kwargs, dyn_args, dyn_kwargs,
+                          lineno=token.lineno)
+
+    def parse_filter(self, node, start_inline=False):
+        while self.stream.current.type == 'pipe' or start_inline:
+            if not start_inline:
+                next(self.stream)
+            token = self.stream.expect('name')
+            name = token.value
+            while self.stream.current.type == 'dot':
+                next(self.stream)
+                name += '.' + self.stream.expect('name').value
+            if self.stream.current.type == 'lparen':
+                args, kwargs, dyn_args, dyn_kwargs = self.parse_call(None)
+            else:
+                args = []
+                kwargs = []
+                dyn_args = dyn_kwargs = None
+            node = nodes.Filter(node, name, args, kwargs, dyn_args,
+                                dyn_kwargs, lineno=token.lineno)
+            start_inline = False
+        return node
+
+    def parse_test(self, node):
+        token = next(self.stream)
+        if self.stream.current.test('name:not'):
+            next(self.stream)
+            negated = True
+        else:
+            negated = False
+        name = self.stream.expect('name').value
+        while self.stream.current.type == 'dot':
+            next(self.stream)
+            name += '.' + self.stream.expect('name').value
+        dyn_args = dyn_kwargs = None
+        kwargs = []
+        if self.stream.current.type == 'lparen':
+            args, kwargs, dyn_args, dyn_kwargs = self.parse_call(None)
+        elif (self.stream.current.type in ('name', 'string', 'integer',
+                                           'float', 'lparen', 'lbracket',
+                                           'lbrace') and not
+              self.stream.current.test_any('name:else', 'name:or',
+                                           'name:and')):
+            if self.stream.current.test('name:is'):
+                self.fail('You cannot chain multiple tests with is')
+            arg_node = self.parse_primary()
+            arg_node = self.parse_postfix(arg_node)
+            args = [arg_node]
+        else:
+            args = []
+        node = nodes.Test(node, name, args, kwargs, dyn_args,
+                          dyn_kwargs, lineno=token.lineno)
+        if negated:
+            node = nodes.Not(node, lineno=token.lineno)
+        return node
+
+    def subparse(self, end_tokens=None):
+        body = []
+        data_buffer = []
+        add_data = data_buffer.append
+
+        if end_tokens is not None:
+            self._end_token_stack.append(end_tokens)
+
+        def flush_data():
+            if data_buffer:
+                lineno = data_buffer[0].lineno
+                body.append(nodes.Output(data_buffer[:], lineno=lineno))
+                del data_buffer[:]
+
+        try:
+            while self.stream:
+                token = self.stream.current
+                if token.type == 'data':
+                    if token.value:
+                        add_data(nodes.TemplateData(token.value,
+                                                    lineno=token.lineno))
+                    next(self.stream)
+                elif token.type == 'variable_begin':
+                    next(self.stream)
+                    add_data(self.parse_tuple(with_condexpr=True))
+                    self.stream.expect('variable_end')
+                elif token.type == 'block_begin':
+                    flush_data()
+                    next(self.stream)
+                    if end_tokens is not None and \
+                       self.stream.current.test_any(*end_tokens):
+                        return body
+                    rv = self.parse_statement()
+                    if isinstance(rv, list):
+                        body.extend(rv)
+                    else:
+                        body.append(rv)
+                    self.stream.expect('block_end')
+                else:
+                    raise AssertionError('internal parsing error')
+
+            flush_data()
+        finally:
+            if end_tokens is not None:
+                self._end_token_stack.pop()
+
+        return body
+
+    def parse(self):
+        """Parse the whole template into a `Template` node."""
+        result = nodes.Template(self.subparse(), lineno=1)
+        result.set_environment(self.environment)
+        return result
diff --git a/src/jinja2/runtime.py b/src/jinja2/runtime.py
new file mode 100644
index 0000000..19ff838
--- /dev/null
+++ b/src/jinja2/runtime.py
@@ -0,0 +1,906 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.runtime
+    ~~~~~~~~~~~~~~
+
+    Runtime helpers.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+import sys
+
+from itertools import chain
+from types import MethodType
+
+from jinja2.nodes import EvalContext
+from jinja2.utils import Markup, soft_unicode, escape, missing, concat, \
+     internalcode, object_type_repr, evalcontextfunction, Namespace
+from jinja2.exceptions import UndefinedError, TemplateRuntimeError, \
+     TemplateNotFound
+from jinja2._compat import imap, text_type, iteritems, \
+     implements_iterator, implements_to_string, string_types, PY2, \
+     with_metaclass, abc
+
+
+# these variables are exported to the template runtime
+__all__ = ['LoopContext', 'TemplateReference', 'Macro', 'Markup',
+           'TemplateRuntimeError', 'missing', 'concat', 'escape',
+           'markup_join', 'unicode_join', 'to_string', 'identity',
+           'TemplateNotFound', 'Namespace', 'Undefined']
+
+#: the name of the function that is used to convert something into
+#: a string.  We can just use the text type here.
+to_string = text_type
+
+#: the identity function.  Useful for certain things in the environment
+identity = lambda x: x
+
+_first_iteration = object()
+_last_iteration = object()
+
+
+def markup_join(seq):
+    """Concatenation that escapes if necessary and converts to unicode."""
+    buf = []
+    iterator = imap(soft_unicode, seq)
+    for arg in iterator:
+        buf.append(arg)
+        if hasattr(arg, '__html__'):
+            return Markup(u'').join(chain(buf, iterator))
+    return concat(buf)
+
+
+def unicode_join(seq):
+    """Simple args to unicode conversion and concatenation."""
+    return concat(imap(text_type, seq))
+
+
+def new_context(environment, template_name, blocks, vars=None,
+                shared=None, globals=None, locals=None):
+    """Internal helper for context creation."""
+    if vars is None:
+        vars = {}
+    if shared:
+        parent = vars
+    else:
+        parent = dict(globals or (), **vars)
+    if locals:
+        # if the parent is shared a copy should be created because
+        # we don't want to modify the dict passed
+        if shared:
+            parent = dict(parent)
+        for key, value in iteritems(locals):
+            if value is not missing:
+                parent[key] = value
+    return environment.context_class(environment, parent, template_name,
+                                     blocks)
+
+
+class TemplateReference(object):
+    """The `self` in templates."""
+
+    def __init__(self, context):
+        self.__context = context
+
+    def __getitem__(self, name):
+        blocks = self.__context.blocks[name]
+        return BlockReference(name, self.__context, blocks, 0)
+
+    def __repr__(self):
+        return '<%s %r>' % (
+            self.__class__.__name__,
+            self.__context.name
+        )
+
+
+def _get_func(x):
+    return getattr(x, '__func__', x)
+
+
+class ContextMeta(type):
+
+    def __new__(cls, name, bases, d):
+        rv = type.__new__(cls, name, bases, d)
+        if bases == ():
+            return rv
+
+        resolve = _get_func(rv.resolve)
+        default_resolve = _get_func(Context.resolve)
+        resolve_or_missing = _get_func(rv.resolve_or_missing)
+        default_resolve_or_missing = _get_func(Context.resolve_or_missing)
+
+        # If we have a changed resolve but no changed default or missing
+        # resolve we invert the call logic.
+        if resolve is not default_resolve and \
+           resolve_or_missing is default_resolve_or_missing:
+            rv._legacy_resolve_mode = True
+        elif resolve is default_resolve and \
+             resolve_or_missing is default_resolve_or_missing:
+            rv._fast_resolve_mode = True
+
+        return rv
+
+
+def resolve_or_missing(context, key, missing=missing):
+    if key in context.vars:
+        return context.vars[key]
+    if key in context.parent:
+        return context.parent[key]
+    return missing
+
+
+class Context(with_metaclass(ContextMeta)):
+    """The template context holds the variables of a template.  It stores the
+    values passed to the template and also the names the template exports.
+    Creating instances is neither supported nor useful as it's created
+    automatically at various stages of the template evaluation and should not
+    be created by hand.
+
+    The context is immutable.  Modifications on :attr:`parent` **must not**
+    happen and modifications on :attr:`vars` are allowed from generated
+    template code only.  Template filters and global functions marked as
+    :func:`contextfunction`\\s get the active context passed as first argument
+    and are allowed to access the context read-only.
+
+    The template context supports read only dict operations (`get`,
+    `keys`, `values`, `items`, `iterkeys`, `itervalues`, `iteritems`,
+    `__getitem__`, `__contains__`).  Additionally there is a :meth:`resolve`
+    method that doesn't fail with a `KeyError` but returns an
+    :class:`Undefined` object for missing variables.
+    """
+    # XXX: we want to eventually make this be a deprecation warning and
+    # remove it.
+    _legacy_resolve_mode = False
+    _fast_resolve_mode = False
+
+    def __init__(self, environment, parent, name, blocks):
+        self.parent = parent
+        self.vars = {}
+        self.environment = environment
+        self.eval_ctx = EvalContext(self.environment, name)
+        self.exported_vars = set()
+        self.name = name
+
+        # create the initial mapping of blocks.  Whenever template inheritance
+        # takes place the runtime will update this mapping with the new blocks
+        # from the template.
+        self.blocks = dict((k, [v]) for k, v in iteritems(blocks))
+
+        # In case we detect the fast resolve mode we can set up an alias
+        # here that bypasses the legacy code logic.
+        if self._fast_resolve_mode:
+            self.resolve_or_missing = MethodType(resolve_or_missing, self)
+
+    def super(self, name, current):
+        """Render a parent block."""
+        try:
+            blocks = self.blocks[name]
+            index = blocks.index(current) + 1
+            blocks[index]
+        except LookupError:
+            return self.environment.undefined('there is no parent block '
+                                              'called %r.' % name,
+                                              name='super')
+        return BlockReference(name, self, blocks, index)
+
+    def get(self, key, default=None):
+        """Returns an item from the template context, if it doesn't exist
+        `default` is returned.
+        """
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def resolve(self, key):
+        """Looks up a variable like `__getitem__` or `get` but returns an
+        :class:`Undefined` object with the name of the name looked up.
+        """
+        if self._legacy_resolve_mode:
+            rv = resolve_or_missing(self, key)
+        else:
+            rv = self.resolve_or_missing(key)
+        if rv is missing:
+            return self.environment.undefined(name=key)
+        return rv
+
+    def resolve_or_missing(self, key):
+        """Resolves a variable like :meth:`resolve` but returns the
+        special `missing` value if it cannot be found.
+        """
+        if self._legacy_resolve_mode:
+            rv = self.resolve(key)
+            if isinstance(rv, Undefined):
+                rv = missing
+            return rv
+        return resolve_or_missing(self, key)
+
+    def get_exported(self):
+        """Get a new dict with the exported variables."""
+        return dict((k, self.vars[k]) for k in self.exported_vars)
+
+    def get_all(self):
+        """Return the complete context as dict including the exported
+        variables.  For optimizations reasons this might not return an
+        actual copy so be careful with using it.
+        """
+        if not self.vars:
+            return self.parent
+        if not self.parent:
+            return self.vars
+        return dict(self.parent, **self.vars)
+
+    @internalcode
+    def call(__self, __obj, *args, **kwargs):
+        """Call the callable with the arguments and keyword arguments
+        provided but inject the active context or environment as first
+        argument if the callable is a :func:`contextfunction` or
+        :func:`environmentfunction`.
+        """
+        if __debug__:
+            __traceback_hide__ = True  # noqa
+
+        # Allow callable classes to take a context
+        if hasattr(__obj, '__call__'):
+            fn = __obj.__call__
+            for fn_type in ('contextfunction',
+                            'evalcontextfunction',
+                            'environmentfunction'):
+                if hasattr(fn, fn_type):
+                    __obj = fn
+                    break
+
+        if callable(__obj):
+            if getattr(__obj, 'contextfunction', 0):
+                args = (__self,) + args
+            elif getattr(__obj, 'evalcontextfunction', 0):
+                args = (__self.eval_ctx,) + args
+            elif getattr(__obj, 'environmentfunction', 0):
+                args = (__self.environment,) + args
+        try:
+            return __obj(*args, **kwargs)
+        except StopIteration:
+            return __self.environment.undefined('value was undefined because '
+                                                'a callable raised a '
+                                                'StopIteration exception')
+
+    def derived(self, locals=None):
+        """Internal helper function to create a derived context.  This is
+        used in situations where the system needs a new context in the same
+        template that is independent.
+        """
+        context = new_context(self.environment, self.name, {},
+                              self.get_all(), True, None, locals)
+        context.eval_ctx = self.eval_ctx
+        context.blocks.update((k, list(v)) for k, v in iteritems(self.blocks))
+        return context
+
+    def _all(meth):
+        proxy = lambda self: getattr(self.get_all(), meth)()
+        proxy.__doc__ = getattr(dict, meth).__doc__
+        proxy.__name__ = meth
+        return proxy
+
+    keys = _all('keys')
+    values = _all('values')
+    items = _all('items')
+
+    # not available on python 3
+    if PY2:
+        iterkeys = _all('iterkeys')
+        itervalues = _all('itervalues')
+        iteritems = _all('iteritems')
+    del _all
+
+    def __contains__(self, name):
+        return name in self.vars or name in self.parent
+
+    def __getitem__(self, key):
+        """Lookup a variable or raise `KeyError` if the variable is
+        undefined.
+        """
+        item = self.resolve_or_missing(key)
+        if item is missing:
+            raise KeyError(key)
+        return item
+
+    def __repr__(self):
+        return '<%s %s of %r>' % (
+            self.__class__.__name__,
+            repr(self.get_all()),
+            self.name
+        )
+
+
+abc.Mapping.register(Context)
+
+
+class BlockReference(object):
+    """One block on a template reference."""
+
+    def __init__(self, name, context, stack, depth):
+        self.name = name
+        self._context = context
+        self._stack = stack
+        self._depth = depth
+
+    @property
+    def super(self):
+        """Super the block."""
+        if self._depth + 1 >= len(self._stack):
+            return self._context.environment. \
+                undefined('there is no parent block called %r.' %
+                          self.name, name='super')
+        return BlockReference(self.name, self._context, self._stack,
+                              self._depth + 1)
+
+    @internalcode
+    def __call__(self):
+        rv = concat(self._stack[self._depth](self._context))
+        if self._context.eval_ctx.autoescape:
+            rv = Markup(rv)
+        return rv
+
+
+@implements_iterator
+class LoopContext:
+    """A wrapper iterable for dynamic ``for`` loops, with information
+    about the loop and iteration.
+    """
+
+    #: Current iteration of the loop, starting at 0.
+    index0 = -1
+
+    _length = None
+    _after = missing
+    _current = missing
+    _before = missing
+    _last_changed_value = missing
+
+    def __init__(self, iterable, undefined, recurse=None, depth0=0):
+        """
+        :param iterable: Iterable to wrap.
+        :param undefined: :class:`Undefined` class to use for next and
+            previous items.
+        :param recurse: The function to render the loop body when the
+            loop is marked recursive.
+        :param depth0: Incremented when looping recursively.
+        """
+        self._iterable = iterable
+        self._iterator = self._to_iterator(iterable)
+        self._undefined = undefined
+        self._recurse = recurse
+        #: How many levels deep a recursive loop currently is, starting at 0.
+        self.depth0 = depth0
+
+    @staticmethod
+    def _to_iterator(iterable):
+        return iter(iterable)
+
+    @property
+    def length(self):
+        """Length of the iterable.
+
+        If the iterable is a generator or otherwise does not have a
+        size, it is eagerly evaluated to get a size.
+        """
+        if self._length is not None:
+            return self._length
+
+        try:
+            self._length = len(self._iterable)
+        except TypeError:
+            iterable = list(self._iterator)
+            self._iterator = self._to_iterator(iterable)
+            self._length = len(iterable) + self.index + (self._after is not missing)
+
+        return self._length
+
+    def __len__(self):
+        return self.length
+
+    @property
+    def depth(self):
+        """How many levels deep a recursive loop currently is, starting at 1."""
+        return self.depth0 + 1
+
+    @property
+    def index(self):
+        """Current iteration of the loop, starting at 1."""
+        return self.index0 + 1
+
+    @property
+    def revindex0(self):
+        """Number of iterations from the end of the loop, ending at 0.
+
+        Requires calculating :attr:`length`.
+        """
+        return self.length - self.index
+
+    @property
+    def revindex(self):
+        """Number of iterations from the end of the loop, ending at 1.
+
+        Requires calculating :attr:`length`.
+        """
+        return self.length - self.index0
+
+    @property
+    def first(self):
+        """Whether this is the first iteration of the loop."""
+        return self.index0 == 0
+
+    def _peek_next(self):
+        """Return the next element in the iterable, or :data:`missing`
+        if the iterable is exhausted. Only peeks one item ahead, caching
+        the result in :attr:`_last` for use in subsequent checks. The
+        cache is reset when :meth:`__next__` is called.
+        """
+        if self._after is not missing:
+            return self._after
+
+        self._after = next(self._iterator, missing)
+        return self._after
+
+    @property
+    def last(self):
+        """Whether this is the last iteration of the loop.
+
+        Causes the iterable to advance early. See
+        :func:`itertools.groupby` for issues this can cause.
+        The :func:`groupby` filter avoids that issue.
+        """
+        return self._peek_next() is missing
+
+    @property
+    def previtem(self):
+        """The item in the previous iteration. Undefined during the
+        first iteration.
+        """
+        if self.first:
+            return self._undefined("there is no previous item")
+
+        return self._before
+
+    @property
+    def nextitem(self):
+        """The item in the next iteration. Undefined during the last
+        iteration.
+
+        Causes the iterable to advance early. See
+        :func:`itertools.groupby` for issues this can cause.
+        The :func:`groupby` filter avoids that issue.
+        """
+        rv = self._peek_next()
+
+        if rv is missing:
+            return self._undefined("there is no next item")
+
+        return rv
+
+    def cycle(self, *args):
+        """Return a value from the given args, cycling through based on
+        the current :attr:`index0`.
+
+        :param args: One or more values to cycle through.
+        """
+        if not args:
+            raise TypeError("no items for cycling given")
+
+        return args[self.index0 % len(args)]
+
+    def changed(self, *value):
+        """Return ``True`` if previously called with a different value
+        (including when called for the first time).
+
+        :param value: One or more values to compare to the last call.
+        """
+        if self._last_changed_value != value:
+            self._last_changed_value = value
+            return True
+
+        return False
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if self._after is not missing:
+            rv = self._after
+            self._after = missing
+        else:
+            rv = next(self._iterator)
+
+        self.index0 += 1
+        self._before = self._current
+        self._current = rv
+        return rv, self
+
+    @internalcode
+    def __call__(self, iterable):
+        """When iterating over nested data, render the body of the loop
+        recursively with the given inner iterable data.
+
+        The loop must have the ``recursive`` marker for this to work.
+        """
+        if self._recurse is None:
+            raise TypeError(
+                "The loop must have the 'recursive' marker to be"
+                " called recursively."
+            )
+
+        return self._recurse(iterable, self._recurse, depth=self.depth)
+
+    def __repr__(self):
+        return "<%s %d/%d>" % (self.__class__.__name__, self.index, self.length)
+
+
+class Macro(object):
+    """Wraps a macro function."""
+
+    def __init__(self, environment, func, name, arguments,
+                 catch_kwargs, catch_varargs, caller,
+                 default_autoescape=None):
+        self._environment = environment
+        self._func = func
+        self._argument_count = len(arguments)
+        self.name = name
+        self.arguments = arguments
+        self.catch_kwargs = catch_kwargs
+        self.catch_varargs = catch_varargs
+        self.caller = caller
+        self.explicit_caller = 'caller' in arguments
+        if default_autoescape is None:
+            default_autoescape = environment.autoescape
+        self._default_autoescape = default_autoescape
+
+    @internalcode
+    @evalcontextfunction
+    def __call__(self, *args, **kwargs):
+        # This requires a bit of explanation,  In the past we used to
+        # decide largely based on compile-time information if a macro is
+        # safe or unsafe.  While there was a volatile mode it was largely
+        # unused for deciding on escaping.  This turns out to be
+        # problematic for macros because whether a macro is safe depends not
+        # on the escape mode when it was defined, but rather when it was used.
+        #
+        # Because however we export macros from the module system and
+        # there are historic callers that do not pass an eval context (and
+        # will continue to not pass one), we need to perform an instance
+        # check here.
+        #
+        # This is considered safe because an eval context is not a valid
+        # argument to callables otherwise anyway.  Worst case here is
+        # that if no eval context is passed we fall back to the compile
+        # time autoescape flag.
+        if args and isinstance(args[0], EvalContext):
+            autoescape = args[0].autoescape
+            args = args[1:]
+        else:
+            autoescape = self._default_autoescape
+
+        # try to consume the positional arguments
+        arguments = list(args[:self._argument_count])
+        off = len(arguments)
+
+        # For information why this is necessary refer to the handling
+        # of caller in the `macro_body` handler in the compiler.
+        found_caller = False
+
+        # if the number of arguments consumed is not the number of
+        # arguments expected we start filling in keyword arguments
+        # and defaults.
+        if off != self._argument_count:
+            for idx, name in enumerate(self.arguments[len(arguments):]):
+                try:
+                    value = kwargs.pop(name)
+                except KeyError:
+                    value = missing
+                if name == 'caller':
+                    found_caller = True
+                arguments.append(value)
+        else:
+            found_caller = self.explicit_caller
+
+        # it's important that the order of these arguments does not change
+        # if not also changed in the compiler's `function_scoping` method.
+        # the order is caller, keyword arguments, positional arguments!
+        if self.caller and not found_caller:
+            caller = kwargs.pop('caller', None)
+            if caller is None:
+                caller = self._environment.undefined('No caller defined',
+                                                     name='caller')
+            arguments.append(caller)
+
+        if self.catch_kwargs:
+            arguments.append(kwargs)
+        elif kwargs:
+            if 'caller' in kwargs:
+                raise TypeError('macro %r was invoked with two values for '
+                                'the special caller argument.  This is '
+                                'most likely a bug.' % self.name)
+            raise TypeError('macro %r takes no keyword argument %r' %
+                            (self.name, next(iter(kwargs))))
+        if self.catch_varargs:
+            arguments.append(args[self._argument_count:])
+        elif len(args) > self._argument_count:
+            raise TypeError('macro %r takes not more than %d argument(s)' %
+                            (self.name, len(self.arguments)))
+
+        return self._invoke(arguments, autoescape)
+
+    def _invoke(self, arguments, autoescape):
+        """This method is being swapped out by the async implementation."""
+        rv = self._func(*arguments)
+        if autoescape:
+            rv = Markup(rv)
+        return rv
+
+    def __repr__(self):
+        return '<%s %s>' % (
+            self.__class__.__name__,
+            self.name is None and 'anonymous' or repr(self.name)
+        )
+
+
+@implements_to_string
+class Undefined(object):
+    """The default undefined type.  This undefined type can be printed and
+    iterated over, but every other access will raise an :exc:`UndefinedError`:
+
+    >>> foo = Undefined(name='foo')
+    >>> str(foo)
+    ''
+    >>> not foo
+    True
+    >>> foo + 42
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+    """
+    __slots__ = ('_undefined_hint', '_undefined_obj', '_undefined_name',
+                 '_undefined_exception')
+
+    def __init__(self, hint=None, obj=missing, name=None, exc=UndefinedError):
+        self._undefined_hint = hint
+        self._undefined_obj = obj
+        self._undefined_name = name
+        self._undefined_exception = exc
+
+    @property
+    def _undefined_message(self):
+        """Build a message about the undefined value based on how it was
+        accessed.
+        """
+        if self._undefined_hint:
+            return self._undefined_hint
+
+        if self._undefined_obj is missing:
+            return '%r is undefined' % self._undefined_name
+
+        if not isinstance(self._undefined_name, string_types):
+            return '%s has no element %r' % (
+                object_type_repr(self._undefined_obj),
+                self._undefined_name
+            )
+
+        return '%r has no attribute %r' % (
+            object_type_repr(self._undefined_obj),
+            self._undefined_name
+        )
+
+    @internalcode
+    def _fail_with_undefined_error(self, *args, **kwargs):
+        """Raise an :exc:`UndefinedError` when operations are performed
+        on the undefined value.
+        """
+        raise self._undefined_exception(self._undefined_message)
+
+    @internalcode
+    def __getattr__(self, name):
+        if name[:2] == '__':
+            raise AttributeError(name)
+        return self._fail_with_undefined_error()
+
+    __add__ = __radd__ = __mul__ = __rmul__ = __div__ = __rdiv__ = \
+        __truediv__ = __rtruediv__ = __floordiv__ = __rfloordiv__ = \
+        __mod__ = __rmod__ = __pos__ = __neg__ = __call__ = \
+        __getitem__ = __lt__ = __le__ = __gt__ = __ge__ = __int__ = \
+        __float__ = __complex__ = __pow__ = __rpow__ = __sub__ = \
+        __rsub__ = _fail_with_undefined_error
+
+    def __eq__(self, other):
+        return type(self) is type(other)
+
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
+    def __hash__(self):
+        return id(type(self))
+
+    def __str__(self):
+        return u''
+
+    def __len__(self):
+        return 0
+
+    def __iter__(self):
+        if 0:
+            yield None
+
+    def __nonzero__(self):
+        return False
+    __bool__ = __nonzero__
+
+    def __repr__(self):
+        return 'Undefined'
+
+
+def make_logging_undefined(logger=None, base=None):
+    """Given a logger object this returns a new undefined class that will
+    log certain failures.  It will log iterations and printing.  If no
+    logger is given a default logger is created.
+
+    Example::
+
+        logger = logging.getLogger(__name__)
+        LoggingUndefined = make_logging_undefined(
+            logger=logger,
+            base=Undefined
+        )
+
+    .. versionadded:: 2.8
+
+    :param logger: the logger to use.  If not provided, a default logger
+                   is created.
+    :param base: the base class to add logging functionality to.  This
+                 defaults to :class:`Undefined`.
+    """
+    if logger is None:
+        import logging
+        logger = logging.getLogger(__name__)
+        logger.addHandler(logging.StreamHandler(sys.stderr))
+    if base is None:
+        base = Undefined
+
+    def _log_message(undef):
+        if undef._undefined_hint is None:
+            if undef._undefined_obj is missing:
+                hint = '%s is undefined' % undef._undefined_name
+            elif not isinstance(undef._undefined_name, string_types):
+                hint = '%s has no element %s' % (
+                    object_type_repr(undef._undefined_obj),
+                    undef._undefined_name)
+            else:
+                hint = '%s has no attribute %s' % (
+                    object_type_repr(undef._undefined_obj),
+                    undef._undefined_name)
+        else:
+            hint = undef._undefined_hint
+        logger.warning('Template variable warning: %s', hint)
+
+    class LoggingUndefined(base):
+
+        def _fail_with_undefined_error(self, *args, **kwargs):
+            try:
+                return base._fail_with_undefined_error(self, *args, **kwargs)
+            except self._undefined_exception as e:
+                logger.error('Template variable error: %s', str(e))
+                raise e
+
+        def __str__(self):
+            rv = base.__str__(self)
+            _log_message(self)
+            return rv
+
+        def __iter__(self):
+            rv = base.__iter__(self)
+            _log_message(self)
+            return rv
+
+        if PY2:
+            def __nonzero__(self):
+                rv = base.__nonzero__(self)
+                _log_message(self)
+                return rv
+
+            def __unicode__(self):
+                rv = base.__unicode__(self)
+                _log_message(self)
+                return rv
+        else:
+            def __bool__(self):
+                rv = base.__bool__(self)
+                _log_message(self)
+                return rv
+
+    return LoggingUndefined
+
+
+# No @implements_to_string decorator here because __str__
+# is not overwritten from Undefined in this class.
+# This would cause a recursion error in Python 2.
+class ChainableUndefined(Undefined):
+    """An undefined that is chainable, where both ``__getattr__`` and
+    ``__getitem__`` return itself rather than raising an
+    :exc:`UndefinedError`.
+
+    >>> foo = ChainableUndefined(name='foo')
+    >>> str(foo.bar['baz'])
+    ''
+    >>> foo.bar['baz'] + 42
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+
+    .. versionadded:: 2.11.0
+    """
+    __slots__ = ()
+
+    def __html__(self):
+        return self.__str__()
+
+    def __getattr__(self, _):
+        return self
+
+    __getitem__ = __getattr__
+
+
+@implements_to_string
+class DebugUndefined(Undefined):
+    """An undefined that returns the debug info when printed.
+
+    >>> foo = DebugUndefined(name='foo')
+    >>> str(foo)
+    '{{ foo }}'
+    >>> not foo
+    True
+    >>> foo + 42
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+    """
+    __slots__ = ()
+
+    def __str__(self):
+        if self._undefined_hint is None:
+            if self._undefined_obj is missing:
+                return u'{{ %s }}' % self._undefined_name
+            return '{{ no such element: %s[%r] }}' % (
+                object_type_repr(self._undefined_obj),
+                self._undefined_name
+            )
+        return u'{{ undefined value printed: %s }}' % self._undefined_hint
+
+
+@implements_to_string
+class StrictUndefined(Undefined):
+    """An undefined that barks on print and iteration as well as boolean
+    tests and all kinds of comparisons.  In other words: you can do nothing
+    with it except checking if it's defined using the `defined` test.
+
+    >>> foo = StrictUndefined(name='foo')
+    >>> str(foo)
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+    >>> not foo
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+    >>> foo + 42
+    Traceback (most recent call last):
+      ...
+    jinja2.exceptions.UndefinedError: 'foo' is undefined
+    """
+    __slots__ = ()
+    __iter__ = __str__ = __len__ = __nonzero__ = __eq__ = \
+        __ne__ = __bool__ = __hash__ = \
+        Undefined._fail_with_undefined_error
+
+
+# remove remaining slots attributes, after the metaclass did the magic they
+# are unneeded and irritating as they contain wrong data for the subclasses.
+del Undefined.__slots__, ChainableUndefined.__slots__, \
+    DebugUndefined.__slots__, StrictUndefined.__slots__
diff --git a/src/jinja2/sandbox.py b/src/jinja2/sandbox.py
new file mode 100644
index 0000000..6a1f286
--- /dev/null
+++ b/src/jinja2/sandbox.py
@@ -0,0 +1,488 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.sandbox
+    ~~~~~~~~~~~~~~
+
+    Adds a sandbox layer to Jinja as it was the default behavior in the old
+    Jinja 1 releases.  This sandbox is slightly different from Jinja 1 as the
+    default behavior is easier to use.
+
+    The behavior can be changed by subclassing the environment.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+import types
+import operator
+from jinja2.environment import Environment
+from jinja2.exceptions import SecurityError
+from jinja2._compat import string_types, PY2, abc, range_type
+from jinja2.utils import Markup
+
+from markupsafe import EscapeFormatter
+from string import Formatter
+
+
+#: maximum number of items a range may produce
+MAX_RANGE = 100000
+
+#: attributes of function objects that are considered unsafe.
+if PY2:
+    UNSAFE_FUNCTION_ATTRIBUTES = set(['func_closure', 'func_code', 'func_dict',
+                                      'func_defaults', 'func_globals'])
+else:
+    # On versions > python 2 the special attributes on functions are gone,
+    # but they remain on methods and generators for whatever reason.
+    UNSAFE_FUNCTION_ATTRIBUTES = set()
+
+
+#: unsafe method attributes.  function attributes are unsafe for methods too
+UNSAFE_METHOD_ATTRIBUTES = set(['im_class', 'im_func', 'im_self'])
+
+#: unsafe generator attributes.
+UNSAFE_GENERATOR_ATTRIBUTES = set(['gi_frame', 'gi_code'])
+
+#: unsafe attributes on coroutines
+UNSAFE_COROUTINE_ATTRIBUTES = set(['cr_frame', 'cr_code'])
+
+#: unsafe attributes on async generators
+UNSAFE_ASYNC_GENERATOR_ATTRIBUTES = set(['ag_code', 'ag_frame'])
+
+import warnings
+
+# make sure we don't warn in python 2.6 about stuff we don't care about
+warnings.filterwarnings('ignore', 'the sets module', DeprecationWarning,
+                        module='jinja2.sandbox')
+
+from collections import deque
+
+_mutable_set_types = (set,)
+_mutable_mapping_types = (dict,)
+_mutable_sequence_types = (list,)
+
+
+# on python 2.x we can register the user collection types
+try:
+    from UserDict import UserDict, DictMixin
+    from UserList import UserList
+    _mutable_mapping_types += (UserDict, DictMixin)
+    _mutable_set_types += (UserList,)
+except ImportError:
+    pass
+
+# if sets is still available, register the mutable set from there as well
+try:
+    from sets import Set
+    _mutable_set_types += (Set,)
+except ImportError:
+    pass
+
+#: register Python 2.6 abstract base classes
+_mutable_set_types += (abc.MutableSet,)
+_mutable_mapping_types += (abc.MutableMapping,)
+_mutable_sequence_types += (abc.MutableSequence,)
+
+
+_mutable_spec = (
+    (_mutable_set_types, frozenset([
+        'add', 'clear', 'difference_update', 'discard', 'pop', 'remove',
+        'symmetric_difference_update', 'update'
+    ])),
+    (_mutable_mapping_types, frozenset([
+        'clear', 'pop', 'popitem', 'setdefault', 'update'
+    ])),
+    (_mutable_sequence_types, frozenset([
+        'append', 'reverse', 'insert', 'sort', 'extend', 'remove'
+    ])),
+    (deque, frozenset([
+        'append', 'appendleft', 'clear', 'extend', 'extendleft', 'pop',
+        'popleft', 'remove', 'rotate'
+    ]))
+)
+
+
+class _MagicFormatMapping(abc.Mapping):
+    """This class implements a dummy wrapper to fix a bug in the Python
+    standard library for string formatting.
+
+    See https://bugs.python.org/issue13598 for information about why
+    this is necessary.
+    """
+
+    def __init__(self, args, kwargs):
+        self._args = args
+        self._kwargs = kwargs
+        self._last_index = 0
+
+    def __getitem__(self, key):
+        if key == '':
+            idx = self._last_index
+            self._last_index += 1
+            try:
+                return self._args[idx]
+            except LookupError:
+                pass
+            key = str(idx)
+        return self._kwargs[key]
+
+    def __iter__(self):
+        return iter(self._kwargs)
+
+    def __len__(self):
+        return len(self._kwargs)
+
+
+def inspect_format_method(callable):
+    if not isinstance(callable, (types.MethodType,
+                                 types.BuiltinMethodType)) or \
+       callable.__name__ not in ('format', 'format_map'):
+        return None
+    obj = callable.__self__
+    if isinstance(obj, string_types):
+        return obj
+
+
+def safe_range(*args):
+    """A range that can't generate ranges with a length of more than
+    MAX_RANGE items.
+    """
+    rng = range_type(*args)
+
+    if len(rng) > MAX_RANGE:
+        raise OverflowError(
+            "Range too big. The sandbox blocks ranges larger than"
+            " MAX_RANGE (%d)." % MAX_RANGE
+        )
+
+    return rng
+
+
+def unsafe(f):
+    """Marks a function or method as unsafe.
+
+    ::
+
+        @unsafe
+        def delete(self):
+            pass
+    """
+    f.unsafe_callable = True
+    return f
+
+
+def is_internal_attribute(obj, attr):
+    """Test if the attribute given is an internal python attribute.  For
+    example this function returns `True` for the `func_code` attribute of
+    python objects.  This is useful if the environment method
+    :meth:`~SandboxedEnvironment.is_safe_attribute` is overridden.
+
+    >>> from jinja2.sandbox import is_internal_attribute
+    >>> is_internal_attribute(str, "mro")
+    True
+    >>> is_internal_attribute(str, "upper")
+    False
+    """
+    if isinstance(obj, types.FunctionType):
+        if attr in UNSAFE_FUNCTION_ATTRIBUTES:
+            return True
+    elif isinstance(obj, types.MethodType):
+        if attr in UNSAFE_FUNCTION_ATTRIBUTES or \
+           attr in UNSAFE_METHOD_ATTRIBUTES:
+            return True
+    elif isinstance(obj, type):
+        if attr == 'mro':
+            return True
+    elif isinstance(obj, (types.CodeType, types.TracebackType, types.FrameType)):
+        return True
+    elif isinstance(obj, types.GeneratorType):
+        if attr in UNSAFE_GENERATOR_ATTRIBUTES:
+            return True
+    elif hasattr(types, 'CoroutineType') and isinstance(obj, types.CoroutineType):
+        if attr in UNSAFE_COROUTINE_ATTRIBUTES:
+            return True
+    elif hasattr(types, 'AsyncGeneratorType') and isinstance(obj, types.AsyncGeneratorType):
+        if attr in UNSAFE_ASYNC_GENERATOR_ATTRIBUTES:
+            return True
+    return attr.startswith('__')
+
+
+def modifies_known_mutable(obj, attr):
+    """This function checks if an attribute on a builtin mutable object
+    (list, dict, set or deque) would modify it if called.  It also supports
+    the "user"-versions of the objects (`sets.Set`, `UserDict.*` etc.) and
+    with Python 2.6 onwards the abstract base classes `MutableSet`,
+    `MutableMapping`, and `MutableSequence`.
+
+    >>> modifies_known_mutable({}, "clear")
+    True
+    >>> modifies_known_mutable({}, "keys")
+    False
+    >>> modifies_known_mutable([], "append")
+    True
+    >>> modifies_known_mutable([], "index")
+    False
+
+    If called with an unsupported object (such as unicode) `False` is
+    returned.
+
+    >>> modifies_known_mutable("foo", "upper")
+    False
+    """
+    for typespec, unsafe in _mutable_spec:
+        if isinstance(obj, typespec):
+            return attr in unsafe
+    return False
+
+
+class SandboxedEnvironment(Environment):
+    """The sandboxed environment.  It works like the regular environment but
+    tells the compiler to generate sandboxed code.  Additionally subclasses of
+    this environment may override the methods that tell the runtime what
+    attributes or functions are safe to access.
+
+    If the template tries to access insecure code a :exc:`SecurityError` is
+    raised.  However also other exceptions may occur during the rendering so
+    the caller has to ensure that all exceptions are caught.
+    """
+    sandboxed = True
+
+    #: default callback table for the binary operators.  A copy of this is
+    #: available on each instance of a sandboxed environment as
+    #: :attr:`binop_table`
+    default_binop_table = {
+        '+':        operator.add,
+        '-':        operator.sub,
+        '*':        operator.mul,
+        '/':        operator.truediv,
+        '//':       operator.floordiv,
+        '**':       operator.pow,
+        '%':        operator.mod
+    }
+
+    #: default callback table for the unary operators.  A copy of this is
+    #: available on each instance of a sandboxed environment as
+    #: :attr:`unop_table`
+    default_unop_table = {
+        '+':        operator.pos,
+        '-':        operator.neg
+    }
+
+    #: a set of binary operators that should be intercepted.  Each operator
+    #: that is added to this set (empty by default) is delegated to the
+    #: :meth:`call_binop` method that will perform the operator.  The default
+    #: operator callback is specified by :attr:`binop_table`.
+    #:
+    #: The following binary operators are interceptable:
+    #: ``//``, ``%``, ``+``, ``*``, ``-``, ``/``, and ``**``
+    #:
+    #: The default operation form the operator table corresponds to the
+    #: builtin function.  Intercepted calls are always slower than the native
+    #: operator call, so make sure only to intercept the ones you are
+    #: interested in.
+    #:
+    #: .. versionadded:: 2.6
+    intercepted_binops = frozenset()
+
+    #: a set of unary operators that should be intercepted.  Each operator
+    #: that is added to this set (empty by default) is delegated to the
+    #: :meth:`call_unop` method that will perform the operator.  The default
+    #: operator callback is specified by :attr:`unop_table`.
+    #:
+    #: The following unary operators are interceptable: ``+``, ``-``
+    #:
+    #: The default operation form the operator table corresponds to the
+    #: builtin function.  Intercepted calls are always slower than the native
+    #: operator call, so make sure only to intercept the ones you are
+    #: interested in.
+    #:
+    #: .. versionadded:: 2.6
+    intercepted_unops = frozenset()
+
+    def intercept_unop(self, operator):
+        """Called during template compilation with the name of a unary
+        operator to check if it should be intercepted at runtime.  If this
+        method returns `True`, :meth:`call_unop` is executed for this unary
+        operator.  The default implementation of :meth:`call_unop` will use
+        the :attr:`unop_table` dictionary to perform the operator with the
+        same logic as the builtin one.
+
+        The following unary operators are interceptable: ``+`` and ``-``
+
+        Intercepted calls are always slower than the native operator call,
+        so make sure only to intercept the ones you are interested in.
+
+        .. versionadded:: 2.6
+        """
+        return False
+
+
+    def __init__(self, *args, **kwargs):
+        Environment.__init__(self, *args, **kwargs)
+        self.globals['range'] = safe_range
+        self.binop_table = self.default_binop_table.copy()
+        self.unop_table = self.default_unop_table.copy()
+
+    def is_safe_attribute(self, obj, attr, value):
+        """The sandboxed environment will call this method to check if the
+        attribute of an object is safe to access.  Per default all attributes
+        starting with an underscore are considered private as well as the
+        special attributes of internal python objects as returned by the
+        :func:`is_internal_attribute` function.
+        """
+        return not (attr.startswith('_') or is_internal_attribute(obj, attr))
+
+    def is_safe_callable(self, obj):
+        """Check if an object is safely callable.  Per default a function is
+        considered safe unless the `unsafe_callable` attribute exists and is
+        True.  Override this method to alter the behavior, but this won't
+        affect the `unsafe` decorator from this module.
+        """
+        return not (getattr(obj, 'unsafe_callable', False) or
+                    getattr(obj, 'alters_data', False))
+
+    def call_binop(self, context, operator, left, right):
+        """For intercepted binary operator calls (:meth:`intercepted_binops`)
+        this function is executed instead of the builtin operator.  This can
+        be used to fine tune the behavior of certain operators.
+
+        .. versionadded:: 2.6
+        """
+        return self.binop_table[operator](left, right)
+
+    def call_unop(self, context, operator, arg):
+        """For intercepted unary operator calls (:meth:`intercepted_unops`)
+        this function is executed instead of the builtin operator.  This can
+        be used to fine tune the behavior of certain operators.
+
+        .. versionadded:: 2.6
+        """
+        return self.unop_table[operator](arg)
+
+    def getitem(self, obj, argument):
+        """Subscribe an object from sandboxed code."""
+        try:
+            return obj[argument]
+        except (TypeError, LookupError):
+            if isinstance(argument, string_types):
+                try:
+                    attr = str(argument)
+                except Exception:
+                    pass
+                else:
+                    try:
+                        value = getattr(obj, attr)
+                    except AttributeError:
+                        pass
+                    else:
+                        if self.is_safe_attribute(obj, argument, value):
+                            return value
+                        return self.unsafe_undefined(obj, argument)
+        return self.undefined(obj=obj, name=argument)
+
+    def getattr(self, obj, attribute):
+        """Subscribe an object from sandboxed code and prefer the
+        attribute.  The attribute passed *must* be a bytestring.
+        """
+        try:
+            value = getattr(obj, attribute)
+        except AttributeError:
+            try:
+                return obj[attribute]
+            except (TypeError, LookupError):
+                pass
+        else:
+            if self.is_safe_attribute(obj, attribute, value):
+                return value
+            return self.unsafe_undefined(obj, attribute)
+        return self.undefined(obj=obj, name=attribute)
+
+    def unsafe_undefined(self, obj, attribute):
+        """Return an undefined object for unsafe attributes."""
+        return self.undefined('access to attribute %r of %r '
+                              'object is unsafe.' % (
+            attribute,
+            obj.__class__.__name__
+        ), name=attribute, obj=obj, exc=SecurityError)
+
+    def format_string(self, s, args, kwargs, format_func=None):
+        """If a format call is detected, then this is routed through this
+        method so that our safety sandbox can be used for it.
+        """
+        if isinstance(s, Markup):
+            formatter = SandboxedEscapeFormatter(self, s.escape)
+        else:
+            formatter = SandboxedFormatter(self)
+
+        if format_func is not None and format_func.__name__ == 'format_map':
+            if len(args) != 1 or kwargs:
+                raise TypeError(
+                    'format_map() takes exactly one argument %d given'
+                    % (len(args) + (kwargs is not None))
+                )
+
+            kwargs = args[0]
+            args = None
+
+        kwargs = _MagicFormatMapping(args, kwargs)
+        rv = formatter.vformat(s, args, kwargs)
+        return type(s)(rv)
+
+    def call(__self, __context, __obj, *args, **kwargs):
+        """Call an object from sandboxed code."""
+        fmt = inspect_format_method(__obj)
+        if fmt is not None:
+            return __self.format_string(fmt, args, kwargs, __obj)
+
+        # the double prefixes are to avoid double keyword argument
+        # errors when proxying the call.
+        if not __self.is_safe_callable(__obj):
+            raise SecurityError('%r is not safely callable' % (__obj,))
+        return __context.call(__obj, *args, **kwargs)
+
+
+class ImmutableSandboxedEnvironment(SandboxedEnvironment):
+    """Works exactly like the regular `SandboxedEnvironment` but does not
+    permit modifications on the builtin mutable objects `list`, `set`, and
+    `dict` by using the :func:`modifies_known_mutable` function.
+    """
+
+    def is_safe_attribute(self, obj, attr, value):
+        if not SandboxedEnvironment.is_safe_attribute(self, obj, attr, value):
+            return False
+        return not modifies_known_mutable(obj, attr)
+
+
+# This really is not a public API apparently.
+try:
+    from _string import formatter_field_name_split
+except ImportError:
+    def formatter_field_name_split(field_name):
+        return field_name._formatter_field_name_split()
+
+
+class SandboxedFormatterMixin(object):
+
+    def __init__(self, env):
+        self._env = env
+
+    def get_field(self, field_name, args, kwargs):
+        first, rest = formatter_field_name_split(field_name)
+        obj = self.get_value(first, args, kwargs)
+        for is_attr, i in rest:
+            if is_attr:
+                obj = self._env.getattr(obj, i)
+            else:
+                obj = self._env.getitem(obj, i)
+        return obj, first
+
+class SandboxedFormatter(SandboxedFormatterMixin, Formatter):
+
+    def __init__(self, env):
+        SandboxedFormatterMixin.__init__(self, env)
+        Formatter.__init__(self)
+
+class SandboxedEscapeFormatter(SandboxedFormatterMixin, EscapeFormatter):
+
+    def __init__(self, env, escape):
+        SandboxedFormatterMixin.__init__(self, env)
+        EscapeFormatter.__init__(self, escape)
diff --git a/src/jinja2/tests.py b/src/jinja2/tests.py
new file mode 100644
index 0000000..aeec860
--- /dev/null
+++ b/src/jinja2/tests.py
@@ -0,0 +1,221 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.tests
+    ~~~~~~~~~~~~
+
+    Jinja test functions. Used with the "is" operator.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import operator
+import re
+from jinja2.runtime import Undefined
+from jinja2._compat import text_type, string_types, integer_types, abc
+import decimal
+
+number_re = re.compile(r'^-?\d+(\.\d+)?$')
+regex_type = type(number_re)
+
+
+test_callable = callable
+
+
+def test_odd(value):
+    """Return true if the variable is odd."""
+    return value % 2 == 1
+
+
+def test_even(value):
+    """Return true if the variable is even."""
+    return value % 2 == 0
+
+
+def test_divisibleby(value, num):
+    """Check if a variable is divisible by a number."""
+    return value % num == 0
+
+
+def test_defined(value):
+    """Return true if the variable is defined:
+
+    .. sourcecode:: jinja
+
+        {% if variable is defined %}
+            value of variable: {{ variable }}
+        {% else %}
+            variable is not defined
+        {% endif %}
+
+    See the :func:`default` filter for a simple way to set undefined
+    variables.
+    """
+    return not isinstance(value, Undefined)
+
+
+def test_undefined(value):
+    """Like :func:`defined` but the other way round."""
+    return isinstance(value, Undefined)
+
+
+def test_none(value):
+    """Return true if the variable is none."""
+    return value is None
+
+
+def test_boolean(value):
+    """Return true if the object is a boolean value.
+
+    .. versionadded:: 2.11
+    """
+    return value is True or value is False
+
+
+def test_false(value):
+    """Return true if the object is False.
+
+    .. versionadded:: 2.11
+    """
+    return value is False
+
+
+def test_true(value):
+    """Return true if the object is True.
+
+    .. versionadded:: 2.11
+    """
+    return value is True
+
+
+# NOTE: The existing 'number' test matches booleans and floats
+def test_integer(value):
+    """Return true if the object is an integer.
+
+    .. versionadded:: 2.11
+    """
+    return isinstance(value, integer_types) and value is not True and value is not False
+
+
+# NOTE: The existing 'number' test matches booleans and integers
+def test_float(value):
+    """Return true if the object is a float.
+
+    .. versionadded:: 2.11
+    """
+    return isinstance(value, float)
+
+
+def test_lower(value):
+    """Return true if the variable is lowercased."""
+    return text_type(value).islower()
+
+
+def test_upper(value):
+    """Return true if the variable is uppercased."""
+    return text_type(value).isupper()
+
+
+def test_string(value):
+    """Return true if the object is a string."""
+    return isinstance(value, string_types)
+
+
+def test_mapping(value):
+    """Return true if the object is a mapping (dict etc.).
+
+    .. versionadded:: 2.6
+    """
+    return isinstance(value, abc.Mapping)
+
+
+def test_number(value):
+    """Return true if the variable is a number."""
+    return isinstance(value, integer_types + (float, complex, decimal.Decimal))
+
+
+def test_sequence(value):
+    """Return true if the variable is a sequence. Sequences are variables
+    that are iterable.
+    """
+    try:
+        len(value)
+        value.__getitem__
+    except:
+        return False
+    return True
+
+
+def test_sameas(value, other):
+    """Check if an object points to the same memory address than another
+    object:
+
+    .. sourcecode:: jinja
+
+        {% if foo.attribute is sameas false %}
+            the foo attribute really is the `False` singleton
+        {% endif %}
+    """
+    return value is other
+
+
+def test_iterable(value):
+    """Check if it's possible to iterate over an object."""
+    try:
+        iter(value)
+    except TypeError:
+        return False
+    return True
+
+
+def test_escaped(value):
+    """Check if the value is escaped."""
+    return hasattr(value, '__html__')
+
+
+def test_in(value, seq):
+    """Check if value is in seq.
+
+    .. versionadded:: 2.10
+    """
+    return value in seq
+
+
+TESTS = {
+    'odd':              test_odd,
+    'even':             test_even,
+    'divisibleby':      test_divisibleby,
+    'defined':          test_defined,
+    'undefined':        test_undefined,
+    'none':             test_none,
+    'boolean':          test_boolean,
+    'false':            test_false,
+    'true':             test_true,
+    'integer':          test_integer,
+    'float':            test_float,
+    'lower':            test_lower,
+    'upper':            test_upper,
+    'string':           test_string,
+    'mapping':          test_mapping,
+    'number':           test_number,
+    'sequence':         test_sequence,
+    'iterable':         test_iterable,
+    'callable':         test_callable,
+    'sameas':           test_sameas,
+    'escaped':          test_escaped,
+    'in':               test_in,
+    '==':               operator.eq,
+    'eq':               operator.eq,
+    'equalto':          operator.eq,
+    '!=':               operator.ne,
+    'ne':               operator.ne,
+    '>':                operator.gt,
+    'gt':               operator.gt,
+    'greaterthan':      operator.gt,
+    'ge':               operator.ge,
+    '>=':               operator.ge,
+    '<':                operator.lt,
+    'lt':               operator.lt,
+    'lessthan':         operator.lt,
+    '<=':               operator.le,
+    'le':               operator.le,
+}
diff --git a/src/jinja2/utils.py b/src/jinja2/utils.py
new file mode 100644
index 0000000..49501c7
--- /dev/null
+++ b/src/jinja2/utils.py
@@ -0,0 +1,678 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.utils
+    ~~~~~~~~~~~~
+
+    Utility functions.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD, see LICENSE for more details.
+"""
+import os
+import re
+import json
+import warnings
+from collections import deque
+from threading import Lock
+from jinja2._compat import text_type, string_types, url_quote, abc
+
+
+_word_split_re = re.compile(r'(\s+)')
+_punctuation_re = re.compile(
+    '^(?P<lead>(?:%s)*)(?P<middle>.*?)(?P<trail>(?:%s)*)$' % (
+        '|'.join(map(re.escape, ('(', '<', '&lt;'))),
+        '|'.join(map(re.escape, ('.', ',', ')', '>', '\n', '&gt;')))
+    )
+)
+_simple_email_re = re.compile(r'^\S+@[a-zA-Z0-9._-]+\.[a-zA-Z0-9._-]+$')
+_striptags_re = re.compile(r'(<!--.*?-->|<[^>]*>)')
+_entity_re = re.compile(r'&([^;]+);')
+_letters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+_digits = '0123456789'
+
+# special singleton representing missing values for the runtime
+missing = type('MissingType', (), {'__repr__': lambda x: 'missing'})()
+
+# internal code
+internal_code = set()
+
+concat = u''.join
+
+_slash_escape = '\\/' not in json.dumps('/')
+
+
+def contextfunction(f):
+    """This decorator can be used to mark a function or method context callable.
+    A context callable is passed the active :class:`Context` as first argument when
+    called from the template.  This is useful if a function wants to get access
+    to the context or functions provided on the context object.  For example
+    a function that returns a sorted list of template variables the current
+    template exports could look like this::
+
+        @contextfunction
+        def get_exported_names(context):
+            return sorted(context.exported_vars)
+    """
+    f.contextfunction = True
+    return f
+
+
+def evalcontextfunction(f):
+    """This decorator can be used to mark a function or method as an eval
+    context callable.  This is similar to the :func:`contextfunction`
+    but instead of passing the context, an evaluation context object is
+    passed.  For more information about the eval context, see
+    :ref:`eval-context`.
+
+    .. versionadded:: 2.4
+    """
+    f.evalcontextfunction = True
+    return f
+
+
+def environmentfunction(f):
+    """This decorator can be used to mark a function or method as environment
+    callable.  This decorator works exactly like the :func:`contextfunction`
+    decorator just that the first argument is the active :class:`Environment`
+    and not context.
+    """
+    f.environmentfunction = True
+    return f
+
+
+def internalcode(f):
+    """Marks the function as internally used"""
+    internal_code.add(f.__code__)
+    return f
+
+
+def is_undefined(obj):
+    """Check if the object passed is undefined.  This does nothing more than
+    performing an instance check against :class:`Undefined` but looks nicer.
+    This can be used for custom filters or tests that want to react to
+    undefined variables.  For example a custom default filter can look like
+    this::
+
+        def default(var, default=''):
+            if is_undefined(var):
+                return default
+            return var
+    """
+    from jinja2.runtime import Undefined
+    return isinstance(obj, Undefined)
+
+
+def consume(iterable):
+    """Consumes an iterable without doing anything with it."""
+    for event in iterable:
+        pass
+
+
+def clear_caches():
+    """Jinja keeps internal caches for environments and lexers.  These are
+    used so that Jinja doesn't have to recreate environments and lexers all
+    the time.  Normally you don't have to care about that but if you are
+    measuring memory consumption you may want to clean the caches.
+    """
+    from jinja2.environment import _spontaneous_environments
+    from jinja2.lexer import _lexer_cache
+    _spontaneous_environments.clear()
+    _lexer_cache.clear()
+
+
+def import_string(import_name, silent=False):
+    """Imports an object based on a string.  This is useful if you want to
+    use import paths as endpoints or something similar.  An import path can
+    be specified either in dotted notation (``xml.sax.saxutils.escape``)
+    or with a colon as object delimiter (``xml.sax.saxutils:escape``).
+
+    If the `silent` is True the return value will be `None` if the import
+    fails.
+
+    :return: imported object
+    """
+    try:
+        if ':' in import_name:
+            module, obj = import_name.split(':', 1)
+        elif '.' in import_name:
+            module, _, obj = import_name.rpartition('.')
+        else:
+            return __import__(import_name)
+        return getattr(__import__(module, None, None, [obj]), obj)
+    except (ImportError, AttributeError):
+        if not silent:
+            raise
+
+
+def open_if_exists(filename, mode='rb'):
+    """Returns a file descriptor for the filename if that file exists,
+    otherwise ``None``.
+    """
+    if not os.path.isfile(filename):
+        return None
+
+    return open(filename, mode)
+
+
+def object_type_repr(obj):
+    """Returns the name of the object's type.  For some recognized
+    singletons the name of the object is returned instead. (For
+    example for `None` and `Ellipsis`).
+    """
+    if obj is None:
+        return 'None'
+    elif obj is Ellipsis:
+        return 'Ellipsis'
+    # __builtin__ in 2.x, builtins in 3.x
+    if obj.__class__.__module__ in ('__builtin__', 'builtins'):
+        name = obj.__class__.__name__
+    else:
+        name = obj.__class__.__module__ + '.' + obj.__class__.__name__
+    return '%s object' % name
+
+
+def pformat(obj, verbose=False):
+    """Prettyprint an object.  Either use the `pretty` library or the
+    builtin `pprint`.
+    """
+    try:
+        from pretty import pretty
+        return pretty(obj, verbose=verbose)
+    except ImportError:
+        from pprint import pformat
+        return pformat(obj)
+
+
+def urlize(text, trim_url_limit=None, rel=None, target=None):
+    """Converts any URLs in text into clickable links. Works on http://,
+    https:// and www. links. Links can have trailing punctuation (periods,
+    commas, close-parens) and leading punctuation (opening parens) and
+    it'll still do the right thing.
+
+    If trim_url_limit is not None, the URLs in link text will be limited
+    to trim_url_limit characters.
+
+    If nofollow is True, the URLs in link text will get a rel="nofollow"
+    attribute.
+
+    If target is not None, a target attribute will be added to the link.
+    """
+    trim_url = lambda x, limit=trim_url_limit: limit is not None \
+                         and (x[:limit] + (len(x) >=limit and '...'
+                         or '')) or x
+    words = _word_split_re.split(text_type(escape(text)))
+    rel_attr = rel and ' rel="%s"' % text_type(escape(rel)) or ''
+    target_attr = target and ' target="%s"' % escape(target) or ''
+
+    for i, word in enumerate(words):
+        match = _punctuation_re.match(word)
+        if match:
+            lead, middle, trail = match.groups()
+            if middle.startswith('www.') or (
+                '@' not in middle and
+                not middle.startswith('http://') and
+                not middle.startswith('https://') and
+                len(middle) > 0 and
+                middle[0] in _letters + _digits and (
+                    middle.endswith('.org') or
+                    middle.endswith('.net') or
+                    middle.endswith('.com')
+                )):
+                middle = '<a href="http://%s"%s%s>%s</a>' % (middle,
+                    rel_attr, target_attr, trim_url(middle))
+            if middle.startswith('http://') or \
+               middle.startswith('https://'):
+                middle = '<a href="%s"%s%s>%s</a>' % (middle,
+                    rel_attr, target_attr, trim_url(middle))
+            if '@' in middle and not middle.startswith('www.') and \
+               not ':' in middle and _simple_email_re.match(middle):
+                middle = '<a href="mailto:%s">%s</a>' % (middle, middle)
+            if lead + middle + trail != word:
+                words[i] = lead + middle + trail
+    return u''.join(words)
+
+
+def generate_lorem_ipsum(n=5, html=True, min=20, max=100):
+    """Generate some lorem ipsum for the template."""
+    from jinja2.constants import LOREM_IPSUM_WORDS
+    from random import choice, randrange
+    words = LOREM_IPSUM_WORDS.split()
+    result = []
+
+    for _ in range(n):
+        next_capitalized = True
+        last_comma = last_fullstop = 0
+        word = None
+        last = None
+        p = []
+
+        # each paragraph contains out of 20 to 100 words.
+        for idx, _ in enumerate(range(randrange(min, max))):
+            while True:
+                word = choice(words)
+                if word != last:
+                    last = word
+                    break
+            if next_capitalized:
+                word = word.capitalize()
+                next_capitalized = False
+            # add commas
+            if idx - randrange(3, 8) > last_comma:
+                last_comma = idx
+                last_fullstop += 2
+                word += ','
+            # add end of sentences
+            if idx - randrange(10, 20) > last_fullstop:
+                last_comma = last_fullstop = idx
+                word += '.'
+                next_capitalized = True
+            p.append(word)
+
+        # ensure that the paragraph ends with a dot.
+        p = u' '.join(p)
+        if p.endswith(','):
+            p = p[:-1] + '.'
+        elif not p.endswith('.'):
+            p += '.'
+        result.append(p)
+
+    if not html:
+        return u'\n\n'.join(result)
+    return Markup(u'\n'.join(u'<p>%s</p>' % escape(x) for x in result))
+
+
+def unicode_urlencode(obj, charset="utf-8", for_qs=False):
+    """Quote a string for use in a URL using the given charset.
+
+    This function is misnamed, it is a wrapper around
+    :func:`urllib.parse.quote`.
+
+    :param obj: String or bytes to quote. Other types are converted to
+        string then encoded to bytes using the given charset.
+    :param charset: Encode text to bytes using this charset.
+    :param for_qs: Quote "/" and use "+" for spaces.
+    """
+    if not isinstance(obj, string_types):
+        obj = text_type(obj)
+
+    if isinstance(obj, text_type):
+        obj = obj.encode(charset)
+
+    safe = b"" if for_qs else b"/"
+    rv = url_quote(obj, safe)
+
+    if not isinstance(rv, text_type):
+        rv = rv.decode("utf-8")
+
+    if for_qs:
+        rv = rv.replace("%20", "+")
+
+    return rv
+
+
+class LRUCache(object):
+    """A simple LRU Cache implementation."""
+
+    # this is fast for small capacities (something below 1000) but doesn't
+    # scale.  But as long as it's only used as storage for templates this
+    # won't do any harm.
+
+    def __init__(self, capacity):
+        self.capacity = capacity
+        self._mapping = {}
+        self._queue = deque()
+        self._postinit()
+
+    def _postinit(self):
+        # alias all queue methods for faster lookup
+        self._popleft = self._queue.popleft
+        self._pop = self._queue.pop
+        self._remove = self._queue.remove
+        self._wlock = Lock()
+        self._append = self._queue.append
+
+    def __getstate__(self):
+        return {
+            'capacity':     self.capacity,
+            '_mapping':     self._mapping,
+            '_queue':       self._queue
+        }
+
+    def __setstate__(self, d):
+        self.__dict__.update(d)
+        self._postinit()
+
+    def __getnewargs__(self):
+        return (self.capacity,)
+
+    def copy(self):
+        """Return a shallow copy of the instance."""
+        rv = self.__class__(self.capacity)
+        rv._mapping.update(self._mapping)
+        rv._queue.extend(self._queue)
+        return rv
+
+    def get(self, key, default=None):
+        """Return an item from the cache dict or `default`"""
+        try:
+            return self[key]
+        except KeyError:
+            return default
+
+    def setdefault(self, key, default=None):
+        """Set `default` if the key is not in the cache otherwise
+        leave unchanged. Return the value of this key.
+        """
+        try:
+            return self[key]
+        except KeyError:
+            self[key] = default
+            return default
+
+    def clear(self):
+        """Clear the cache."""
+        self._wlock.acquire()
+        try:
+            self._mapping.clear()
+            self._queue.clear()
+        finally:
+            self._wlock.release()
+
+    def __contains__(self, key):
+        """Check if a key exists in this cache."""
+        return key in self._mapping
+
+    def __len__(self):
+        """Return the current size of the cache."""
+        return len(self._mapping)
+
+    def __repr__(self):
+        return '<%s %r>' % (
+            self.__class__.__name__,
+            self._mapping
+        )
+
+    def __getitem__(self, key):
+        """Get an item from the cache. Moves the item up so that it has the
+        highest priority then.
+
+        Raise a `KeyError` if it does not exist.
+        """
+        self._wlock.acquire()
+        try:
+            rv = self._mapping[key]
+            if self._queue[-1] != key:
+                try:
+                    self._remove(key)
+                except ValueError:
+                    # if something removed the key from the container
+                    # when we read, ignore the ValueError that we would
+                    # get otherwise.
+                    pass
+                self._append(key)
+            return rv
+        finally:
+            self._wlock.release()
+
+    def __setitem__(self, key, value):
+        """Sets the value for an item. Moves the item up so that it
+        has the highest priority then.
+        """
+        self._wlock.acquire()
+        try:
+            if key in self._mapping:
+                self._remove(key)
+            elif len(self._mapping) == self.capacity:
+                del self._mapping[self._popleft()]
+            self._append(key)
+            self._mapping[key] = value
+        finally:
+            self._wlock.release()
+
+    def __delitem__(self, key):
+        """Remove an item from the cache dict.
+        Raise a `KeyError` if it does not exist.
+        """
+        self._wlock.acquire()
+        try:
+            del self._mapping[key]
+            try:
+                self._remove(key)
+            except ValueError:
+                pass
+        finally:
+            self._wlock.release()
+
+    def items(self):
+        """Return a list of items."""
+        result = [(key, self._mapping[key]) for key in list(self._queue)]
+        result.reverse()
+        return result
+
+    def iteritems(self):
+        """Iterate over all items."""
+        return iter(self.items())
+
+    def values(self):
+        """Return a list of all values."""
+        return [x[1] for x in self.items()]
+
+    def itervalue(self):
+        """Iterate over all values."""
+        warnings.warn(DeprecationWarning(
+            '"itervalue()" is deprecated and will be removed in version 2.12.'
+            + ' Use "itervalues()" instead.'
+        ), stacklevel=2)
+        return self.itervalues()
+
+    def itervalues(self):
+        """Iterate over all values."""
+        return iter(self.values())
+
+    def keys(self):
+        """Return a list of all keys ordered by most recent usage."""
+        return list(self)
+
+    def iterkeys(self):
+        """Iterate over all keys in the cache dict, ordered by
+        the most recent usage.
+        """
+        return reversed(tuple(self._queue))
+
+    __iter__ = iterkeys
+
+    def __reversed__(self):
+        """Iterate over the keys in the cache dict, oldest items
+        coming first.
+        """
+        return iter(tuple(self._queue))
+
+    __copy__ = copy
+
+
+abc.MutableMapping.register(LRUCache)
+
+
+def select_autoescape(enabled_extensions=('html', 'htm', 'xml'),
+                      disabled_extensions=(),
+                      default_for_string=True,
+                      default=False):
+    """Intelligently sets the initial value of autoescaping based on the
+    filename of the template.  This is the recommended way to configure
+    autoescaping if you do not want to write a custom function yourself.
+
+    If you want to enable it for all templates created from strings or
+    for all templates with `.html` and `.xml` extensions::
+
+        from jinja2 import Environment, select_autoescape
+        env = Environment(autoescape=select_autoescape(
+            enabled_extensions=('html', 'xml'),
+            default_for_string=True,
+        ))
+
+    Example configuration to turn it on at all times except if the template
+    ends with `.txt`::
+
+        from jinja2 import Environment, select_autoescape
+        env = Environment(autoescape=select_autoescape(
+            disabled_extensions=('txt',),
+            default_for_string=True,
+            default=True,
+        ))
+
+    The `enabled_extensions` is an iterable of all the extensions that
+    autoescaping should be enabled for.  Likewise `disabled_extensions` is
+    a list of all templates it should be disabled for.  If a template is
+    loaded from a string then the default from `default_for_string` is used.
+    If nothing matches then the initial value of autoescaping is set to the
+    value of `default`.
+
+    For security reasons this function operates case insensitive.
+
+    .. versionadded:: 2.9
+    """
+    enabled_patterns = tuple('.' + x.lstrip('.').lower()
+                             for x in enabled_extensions)
+    disabled_patterns = tuple('.' + x.lstrip('.').lower()
+                              for x in disabled_extensions)
+    def autoescape(template_name):
+        if template_name is None:
+            return default_for_string
+        template_name = template_name.lower()
+        if template_name.endswith(enabled_patterns):
+            return True
+        if template_name.endswith(disabled_patterns):
+            return False
+        return default
+    return autoescape
+
+
+def htmlsafe_json_dumps(obj, dumper=None, **kwargs):
+    """Works exactly like :func:`dumps` but is safe for use in ``<script>``
+    tags.  It accepts the same arguments and returns a JSON string.  Note that
+    this is available in templates through the ``|tojson`` filter which will
+    also mark the result as safe.  Due to how this function escapes certain
+    characters this is safe even if used outside of ``<script>`` tags.
+
+    The following characters are escaped in strings:
+
+    -   ``<``
+    -   ``>``
+    -   ``&``
+    -   ``'``
+
+    This makes it safe to embed such strings in any place in HTML with the
+    notable exception of double quoted attributes.  In that case single
+    quote your attributes or HTML escape it in addition.
+    """
+    if dumper is None:
+        dumper = json.dumps
+    rv = dumper(obj, **kwargs) \
+        .replace(u'<', u'\\u003c') \
+        .replace(u'>', u'\\u003e') \
+        .replace(u'&', u'\\u0026') \
+        .replace(u"'", u'\\u0027')
+    return Markup(rv)
+
+
+class Cycler(object):
+    """Cycle through values by yield them one at a time, then restarting
+    once the end is reached. Available as ``cycler`` in templates.
+
+    Similar to ``loop.cycle``, but can be used outside loops or across
+    multiple loops. For example, render a list of folders and files in a
+    list, alternating giving them "odd" and "even" classes.
+
+    .. code-block:: html+jinja
+
+        {% set row_class = cycler("odd", "even") %}
+        <ul class="browser">
+        {% for folder in folders %}
+          <li class="folder {{ row_class.next() }}">{{ folder }}
+        {% endfor %}
+        {% for file in files %}
+          <li class="file {{ row_class.next() }}">{{ file }}
+        {% endfor %}
+        </ul>
+
+    :param items: Each positional argument will be yielded in the order
+        given for each cycle.
+
+    .. versionadded:: 2.1
+    """
+
+    def __init__(self, *items):
+        if not items:
+            raise RuntimeError('at least one item has to be provided')
+        self.items = items
+        self.pos = 0
+
+    def reset(self):
+        """Resets the current item to the first item."""
+        self.pos = 0
+
+    @property
+    def current(self):
+        """Return the current item. Equivalent to the item that will be
+        returned next time :meth:`next` is called.
+        """
+        return self.items[self.pos]
+
+    def next(self):
+        """Return the current item, then advance :attr:`current` to the
+        next item.
+        """
+        rv = self.current
+        self.pos = (self.pos + 1) % len(self.items)
+        return rv
+
+    __next__ = next
+
+
+class Joiner(object):
+    """A joining helper for templates."""
+
+    def __init__(self, sep=u', '):
+        self.sep = sep
+        self.used = False
+
+    def __call__(self):
+        if not self.used:
+            self.used = True
+            return u''
+        return self.sep
+
+
+class Namespace(object):
+    """A namespace object that can hold arbitrary attributes.  It may be
+    initialized from a dictionary or with keyword arguments."""
+
+    def __init__(*args, **kwargs):
+        self, args = args[0], args[1:]
+        self.__attrs = dict(*args, **kwargs)
+
+    def __getattribute__(self, name):
+        if name == '_Namespace__attrs':
+            return object.__getattribute__(self, name)
+        try:
+            return self.__attrs[name]
+        except KeyError:
+            raise AttributeError(name)
+
+    def __setitem__(self, name, value):
+        self.__attrs[name] = value
+
+    def __repr__(self):
+        return '<Namespace %r>' % self.__attrs
+
+
+# does this python version support async for in and async generators?
+try:
+    exec('async def _():\n async for _ in ():\n  yield _')
+    have_async_gen = True
+except SyntaxError:
+    have_async_gen = False
+
+
+# Imported here because that's where it was in the past
+from markupsafe import Markup, escape, soft_unicode
diff --git a/src/jinja2/visitor.py b/src/jinja2/visitor.py
new file mode 100644
index 0000000..ba526df
--- /dev/null
+++ b/src/jinja2/visitor.py
@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+"""
+    jinja2.visitor
+    ~~~~~~~~~~~~~~
+
+    This module implements a visitor for the nodes.
+
+    :copyright: (c) 2017 by the Jinja Team.
+    :license: BSD.
+"""
+from jinja2.nodes import Node
+
+
+class NodeVisitor(object):
+    """Walks the abstract syntax tree and call visitor functions for every
+    node found.  The visitor functions may return values which will be
+    forwarded by the `visit` method.
+
+    Per default the visitor functions for the nodes are ``'visit_'`` +
+    class name of the node.  So a `TryFinally` node visit function would
+    be `visit_TryFinally`.  This behavior can be changed by overriding
+    the `get_visitor` function.  If no visitor function exists for a node
+    (return value `None`) the `generic_visit` visitor is used instead.
+    """
+
+    def get_visitor(self, node):
+        """Return the visitor function for this node or `None` if no visitor
+        exists for this node.  In that case the generic visit function is
+        used instead.
+        """
+        method = 'visit_' + node.__class__.__name__
+        return getattr(self, method, None)
+
+    def visit(self, node, *args, **kwargs):
+        """Visit a node."""
+        f = self.get_visitor(node)
+        if f is not None:
+            return f(node, *args, **kwargs)
+        return self.generic_visit(node, *args, **kwargs)
+
+    def generic_visit(self, node, *args, **kwargs):
+        """Called if no explicit visitor function exists for a node."""
+        for node in node.iter_child_nodes():
+            self.visit(node, *args, **kwargs)
+
+
+class NodeTransformer(NodeVisitor):
+    """Walks the abstract syntax tree and allows modifications of nodes.
+
+    The `NodeTransformer` will walk the AST and use the return value of the
+    visitor functions to replace or remove the old node.  If the return
+    value of the visitor function is `None` the node will be removed
+    from the previous location otherwise it's replaced with the return
+    value.  The return value may be the original node in which case no
+    replacement takes place.
+    """
+
+    def generic_visit(self, node, *args, **kwargs):
+        for field, old_value in node.iter_fields():
+            if isinstance(old_value, list):
+                new_values = []
+                for value in old_value:
+                    if isinstance(value, Node):
+                        value = self.visit(value, *args, **kwargs)
+                        if value is None:
+                            continue
+                        elif not isinstance(value, Node):
+                            new_values.extend(value)
+                            continue
+                    new_values.append(value)
+                old_value[:] = new_values
+            elif isinstance(old_value, Node):
+                new_node = self.visit(old_value, *args, **kwargs)
+                if new_node is None:
+                    delattr(node, field)
+                else:
+                    setattr(node, field, new_node)
+        return node
+
+    def visit_list(self, node, *args, **kwargs):
+        """As transformers may return lists in some places this method
+        can be used to enforce a list as return value.
+        """
+        rv = self.visit(node, *args, **kwargs)
+        if not isinstance(rv, list):
+            rv = [rv]
+        return rv