pygments.scanner.py Maven / Gradle / Ivy
# -*- coding: utf-8 -*-
"""
pygments.scanner
~~~~~~~~~~~~~~~~
This library implements a regex based scanner. Some languages
like Pascal are easy to parse but have some keywords that
depend on the context. Because of this it's impossible to lex
that just by using a regular expression lexer like the
`RegexLexer`.
Have a look at the `DelphiLexer` to get an idea of how to use
this scanner.
:copyright: Copyright 2006-2012 by the Pygments team, see AUTHORS.
:license: BSD, see LICENSE for details.
"""
import re
class EndOfText(RuntimeError):
"""
Raise if end of text is reached and the user
tried to call a match function.
"""
class Scanner(object):
"""
Simple scanner
All method patterns are regular expression strings (not
compiled expressions!)
"""
def __init__(self, text, flags=0):
"""
:param text: The text which should be scanned
:param flags: default regular expression flags
"""
self.data = text
self.data_length = len(text)
self.start_pos = 0
self.pos = 0
self.flags = flags
self.last = None
self.match = None
self._re_cache = {}
def eos(self):
"""`True` if the scanner reached the end of text."""
return self.pos >= self.data_length
eos = property(eos, eos.__doc__)
def check(self, pattern):
"""
Apply `pattern` on the current position and return
the match object. (Doesn't touch pos). Use this for
lookahead.
"""
if self.eos:
raise EndOfText()
if pattern not in self._re_cache:
self._re_cache[pattern] = re.compile(pattern, self.flags)
return self._re_cache[pattern].match(self.data, self.pos)
def test(self, pattern):
"""Apply a pattern on the current position and check
if it patches. Doesn't touch pos."""
return self.check(pattern) is not None
def scan(self, pattern):
"""
Scan the text for the given pattern and update pos/match
and related fields. The return value is a boolen that
indicates if the pattern matched. The matched value is
stored on the instance as ``match``, the last value is
stored as ``last``. ``start_pos`` is the position of the
pointer before the pattern was matched, ``pos`` is the
end position.
"""
if self.eos:
raise EndOfText()
if pattern not in self._re_cache:
self._re_cache[pattern] = re.compile(pattern, self.flags)
self.last = self.match
m = self._re_cache[pattern].match(self.data, self.pos)
if m is None:
return False
self.start_pos = m.start()
self.pos = m.end()
self.match = m.group()
return True
def get_char(self):
"""Scan exactly one char."""
self.scan('.')
def __repr__(self):
return '<%s %d/%d>' % (
self.__class__.__name__,
self.pos,
self.data_length
)