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105 lines
3.0 KiB
105 lines
3.0 KiB
2 years ago
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"""
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pygments.scanner
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~~~~~~~~~~~~~~~~
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This library implements a regex based scanner. Some languages
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like Pascal are easy to parse but have some keywords that
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depend on the context. Because of this it's impossible to lex
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that just by using a regular expression lexer like the
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`RegexLexer`.
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Have a look at the `DelphiLexer` to get an idea of how to use
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this scanner.
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:copyright: Copyright 2006-2022 by the Pygments team, see AUTHORS.
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:license: BSD, see LICENSE for details.
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"""
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import re
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class EndOfText(RuntimeError):
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"""
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Raise if end of text is reached and the user
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tried to call a match function.
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"""
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class Scanner:
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"""
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Simple scanner
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All method patterns are regular expression strings (not
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compiled expressions!)
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"""
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def __init__(self, text, flags=0):
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"""
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:param text: The text which should be scanned
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:param flags: default regular expression flags
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"""
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self.data = text
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self.data_length = len(text)
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self.start_pos = 0
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self.pos = 0
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self.flags = flags
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self.last = None
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self.match = None
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self._re_cache = {}
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def eos(self):
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"""`True` if the scanner reached the end of text."""
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return self.pos >= self.data_length
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eos = property(eos, eos.__doc__)
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def check(self, pattern):
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"""
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Apply `pattern` on the current position and return
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the match object. (Doesn't touch pos). Use this for
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lookahead.
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"""
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if self.eos:
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raise EndOfText()
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if pattern not in self._re_cache:
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self._re_cache[pattern] = re.compile(pattern, self.flags)
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return self._re_cache[pattern].match(self.data, self.pos)
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def test(self, pattern):
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"""Apply a pattern on the current position and check
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if it patches. Doesn't touch pos.
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"""
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return self.check(pattern) is not None
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def scan(self, pattern):
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"""
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Scan the text for the given pattern and update pos/match
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and related fields. The return value is a boolean that
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indicates if the pattern matched. The matched value is
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stored on the instance as ``match``, the last value is
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stored as ``last``. ``start_pos`` is the position of the
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pointer before the pattern was matched, ``pos`` is the
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end position.
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"""
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if self.eos:
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raise EndOfText()
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if pattern not in self._re_cache:
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self._re_cache[pattern] = re.compile(pattern, self.flags)
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self.last = self.match
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m = self._re_cache[pattern].match(self.data, self.pos)
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if m is None:
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return False
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self.start_pos = m.start()
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self.pos = m.end()
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self.match = m.group()
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return True
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def get_char(self):
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"""Scan exactly one char."""
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self.scan('.')
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def __repr__(self):
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return '<%s %d/%d>' % (
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self.__class__.__name__,
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self.pos,
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self.data_length
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)
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