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# Copyright (C) 2006 by Canonical Ltd
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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"""Lazily compiled regex objects.
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This module defines a class which creates proxy objects for regex compilation.
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This allows overriding re.compile() to return lazily compiled objects.
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_real_re_compile = re.compile
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class LazyRegex(object):
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"""A proxy around a real regex, which won't compiled until accessed."""
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# These are the parameters on a real _sre.SRE_Pattern object, which we
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# will map to local members so that we don't have the proxy overhead.
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_regex_attributes_to_copy = [
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'__copy__', '__deepcopy__', 'findall', 'finditer', 'match',
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'scanner', 'search', 'split', 'sub', 'subn'
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# We use slots to keep the overhead low. But we need a slot entry for
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# all of the attributes we will copy
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__slots__ = ['_real_regex', '_regex_args', '_regex_kwargs',
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] + _regex_attributes_to_copy
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def __init__(self, args=(), kwargs={}):
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"""Create a new proxy object, passing in the args to pass to re.compile
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:param args: The *args to pass to re.compile
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:param kwargs: The **kwargs to pass to re.compile
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self._real_regex = None
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self._regex_args = args
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self._regex_kwargs = kwargs
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def _compile_and_collapse(self):
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"""Actually compile the requested regex"""
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self._real_regex = self._real_re_compile(*self._regex_args,
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for attr in self._regex_attributes_to_copy:
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setattr(self, attr, getattr(self._real_regex, attr))
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def _real_re_compile(self, *args, **kwargs):
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"""Thunk over to the original re.compile"""
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return _real_re_compile(*args, **kwargs)
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def __getattr__(self, attr):
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"""Return a member from the proxied regex object.
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If the regex hasn't been compiled yet, compile it
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if self._real_regex is None:
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self._compile_and_collapse()
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# Once we have compiled, the only time we should come here
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# is actually if the attribute is missing.
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return getattr(self._real_regex, attr)
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def lazy_compile(*args, **kwargs):
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"""Create a proxy object which will compile the regex on demand.
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:return: a LazyRegex proxy object.
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return LazyRegex(args, kwargs)
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bzrlib/lazy_regex.py
