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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.parsed import ParsedTemplate
DEFAULT_DELIMITERS = (u'{{', u'}}')
END_OF_LINE_CHARACTERS = [u'\r', u'\n']
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 VariableNode(object):
def __init__(self, key):
self.key = key
def render(self, engine, context):
s = engine._get_string_value(context, self.key)
return engine.escape(s)
class LiteralNode(object):
def __init__(self, key):
self.key = key
def render(self, engine, context):
s = engine._get_string_value(context, self.key)
return engine.literal(s)
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_delimiters(self):
self._template_re = _compile_template_re(self._delimiters)
def _change_delimiters(self, delimiters):
self._delimiters = delimiters
self._compile_delimiters()
def parse(self, template):
"""
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.
"""
self._compile_delimiters()
start_index = 0
content_end_index, parsed_section, section_key = None, None, None
parsed_template = ParsedTemplate()
states = []
while True:
match = self._template_re.search(template, start_index)
if match is None:
break
match_index = match.start()
end_index = match.end()
# Avoid adding spurious empty strings to the parse tree.
if start_index != match_index:
parsed_template.add(template[start_index:match_index])
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:
parsed_template.add(leading_whitespace)
match_index += len(leading_whitespace)
leading_whitespace = ''
start_index = end_index
if tag_type in ('#', '^'):
# Cache current state.
state = (tag_type, end_index, section_key, parsed_template)
states.append(state)
# Initialize new state
section_key, parsed_template = tag_key, ParsedTemplate()
continue
if tag_type == '/':
if tag_key != section_key:
raise ParsingError("Section end tag mismatch: %s != %s" % (tag_key, section_key))
# Restore previous state with newly found section data.
parsed_section = parsed_template
(tag_type, section_start_index, section_key, parsed_template) = states.pop()
node = self._make_section_node(template, tag_type, tag_key, parsed_section,
section_start_index, match_index)
else:
node = self._make_interpolation_node(tag_type, tag_key, leading_whitespace)
parsed_template.add(node)
# Add the remainder of the template.
parsed_template.add(template[start_index:])
return parsed_template
def _make_interpolation_node(self, tag_type, tag_key, leading_whitespace):
"""
Create and return a non-section node for the parse tree.
"""
# TODO: switch to using a dictionary instead of a bunch of ifs and elifs.
if tag_type == '!':
return u''
if tag_type == '=':
delimiters = tag_key.split()
self._change_delimiters(delimiters)
return u''
if tag_type == '':
return VariableNode(tag_key)
if tag_type == '&':
return LiteralNode(tag_key)
if tag_type == '>':
return self.engine._make_get_partial(tag_key, leading_whitespace)
raise Exception("Invalid symbol for interpolation tag: %s" % repr(tag_type))
def _make_section_node(self, template, tag_type, tag_key, parsed_section,
section_start_index, section_end_index):
"""
Create and return a section node for the parse tree.
"""
if tag_type == '#':
return self.engine._make_get_section(tag_key, parsed_section, self._delimiters,
template, section_start_index, section_end_index)
if tag_type == '^':
return self.engine._make_get_inverse(tag_key, parsed_section)
raise Exception("Invalid symbol for section tag: %s" % repr(tag_type))
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