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# coding: utf-8
"""
Provides a class for parsing template strings.
This module is only meant for internal use by the renderengine module.
"""
import re
from pystache.common import TemplateNotFoundError
from pystache.parsed import ParsedTemplate
DEFAULT_DELIMITERS = (u'{{', u'}}')
END_OF_LINE_CHARACTERS = [u'\r', u'\n']
NON_BLANK_RE = re.compile(ur'^(.)', re.M)
def _compile_template_re(delimiters=None):
"""
Return a regular expresssion object (re.RegexObject) instance.
"""
if delimiters is None:
delimiters = DEFAULT_DELIMITERS
# The possible tag type characters following the opening tag,
# excluding "=" and "{".
tag_types = "!>&/#^"
# TODO: are we following this in the spec?
#
# The tag's content MUST be a non-whitespace character sequence
# NOT containing the current closing delimiter.
#
tag = r"""
(?P<whitespace>[\ \t]*)
%(otag)s \s*
(?:
(?P<change>=) \s* (?P<delims>.+?) \s* = |
(?P<raw>{) \s* (?P<raw_name>.+?) \s* } |
(?P<tag>[%(tag_types)s]?) \s* (?P<tag_key>[\s\S]+?)
)
\s* %(ctag)s
""" % {'tag_types': tag_types, 'otag': re.escape(delimiters[0]), 'ctag': re.escape(delimiters[1])}
return re.compile(tag, re.VERBOSE)
class ParsingError(Exception):
pass
class Parser(object):
_delimiters = None
_template_re = None
def __init__(self, engine, delimiters=None):
"""
Construct an instance.
Arguments:
engine: a RenderEngine instance.
"""
if delimiters is None:
delimiters = DEFAULT_DELIMITERS
self._delimiters = delimiters
self.engine = engine
def compile_template_re(self):
self._template_re = _compile_template_re(self._delimiters)
def _change_delimiters(self, delimiters):
self._delimiters = delimiters
self.compile_template_re()
def parse(self, template, start_index=0, section_key=None):
"""
Parse a template string starting at some index.
This method uses the current tag delimiter.
Arguments:
template: a unicode string that is the template to parse.
index: the index at which to start parsing.
Returns:
a ParsedTemplate instance.
"""
parse_tree = []
index = start_index
while True:
match = self._template_re.search(template, index)
if match is None:
break
match_index = match.start()
end_index = match.end()
before_tag = template[index : match_index]
parse_tree.append(before_tag)
matches = match.groupdict()
# Normalize the matches dictionary.
if matches['change'] is not None:
matches.update(tag='=', tag_key=matches['delims'])
elif matches['raw'] is not None:
matches.update(tag='&', tag_key=matches['raw_name'])
tag_type = matches['tag']
tag_key = matches['tag_key']
leading_whitespace = matches['whitespace']
# Standalone (non-interpolation) tags consume the entire line,
# both leading whitespace and trailing newline.
did_tag_begin_line = match_index == 0 or template[match_index - 1] in END_OF_LINE_CHARACTERS
did_tag_end_line = end_index == len(template) or template[end_index] in END_OF_LINE_CHARACTERS
is_tag_interpolating = tag_type in ['', '&']
if did_tag_begin_line and did_tag_end_line and not is_tag_interpolating:
if end_index < len(template):
end_index += template[end_index] == '\r' and 1 or 0
if end_index < len(template):
end_index += template[end_index] == '\n' and 1 or 0
elif leading_whitespace:
parse_tree.append(leading_whitespace)
match_index += len(leading_whitespace)
leading_whitespace = ''
if tag_type == '/':
if tag_key != section_key:
raise ParsingError("Section end tag mismatch: %s != %s" % (tag_key, section_key))
return ParsedTemplate(parse_tree), match_index, end_index
index = self._handle_tag_type(template, parse_tree, tag_type, tag_key, leading_whitespace, end_index)
# Save the rest of the template.
parse_tree.append(template[index:])
return ParsedTemplate(parse_tree)
def _parse_section(self, template, start_index, section_key):
"""
Parse the contents of a template section.
Arguments:
template: a unicode template string.
start_index: the string index at which the section contents begin.
section_key: the tag key of the section.
Returns: a 3-tuple:
parsed_section: the section contents parsed as a ParsedTemplate
instance.
content_end_index: the string index after the section contents.
end_index: the string index after the closing section tag (and
including any trailing newlines).
"""
parsed_section, content_end_index, end_index = \
self.parse(template=template, start_index=start_index, section_key=section_key)
return parsed_section, template[start_index:content_end_index], end_index
def _handle_tag_type(self, template, parse_tree, tag_type, tag_key, leading_whitespace, end_index):
# TODO: switch to using a dictionary instead of a bunch of ifs and elifs.
if tag_type == '!':
return end_index
if tag_type == '=':
delimiters = tag_key.split()
self._change_delimiters(delimiters)
return end_index
engine = self.engine
if tag_type == '':
func = engine._make_get_escaped(tag_key)
elif tag_type == '&':
func = engine._make_get_literal(tag_key)
elif tag_type == '#':
parsed_section, section_contents, end_index = self._parse_section(template, end_index, tag_key)
func = engine._make_get_section(tag_key, parsed_section, section_contents, self._delimiters)
elif tag_type == '^':
parsed_section, section_contents, end_index = self._parse_section(template, end_index, tag_key)
func = engine._make_get_inverse(tag_key, parsed_section)
elif tag_type == '>':
try:
# TODO: make engine.load() and test it separately.
template = engine.load_partial(tag_key)
except TemplateNotFoundError:
template = u''
# Indent before rendering.
template = re.sub(NON_BLANK_RE, leading_whitespace + ur'\1', template)
func = engine._make_get_partial(template)
else:
raise Exception("Unrecognized tag type: %s" % repr(tag_type))
parse_tree.append(func)
return end_index
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