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import types
from ast import literal_eval
from itertools import chain
from itertools import islice
from . import nodes
from .compiler import CodeGenerator
from .compiler import has_safe_repr
from .environment import Environment
from .environment import 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 = "".join([str(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):
quote = raw[0]
return f"{quote}{literal}{quote}"
return literal
class NativeCodeGenerator(CodeGenerator):
"""A code generator which renders Python types by not adding
``str()`` 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
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