~bzr-pqm/bzr/bzr.dev

2052.3.4 by John Arbash Meinel
[merge] bzr.dev
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# Copyright (C) 2006 Canonical Ltd
2063.4.1 by John Arbash Meinel
bzrlib.lazy_regex.lazy_compile creates a proxy object around re.compile()
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#
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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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#
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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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#
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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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
2063.4.1 by John Arbash Meinel
bzrlib.lazy_regex.lazy_compile creates a proxy object around re.compile()
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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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"""
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import re
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class LazyRegex(object):
2063.4.5 by John Arbash Meinel
review feedback from Martin
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    """A proxy around a real regex, which won't be compiled until accessed."""
2063.4.1 by John Arbash Meinel
bzrlib.lazy_regex.lazy_compile creates a proxy object around re.compile()
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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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                 ]
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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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        """
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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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                                                 **self._regex_kwargs)
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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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        """
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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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    """
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    return LazyRegex(args, kwargs)
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2063.4.2 by John Arbash Meinel
Add install and unistall functions, and tests
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def install_lazy_compile():
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    """Make lazy_compile the default compile mode for regex compilation.
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    This overrides re.compile with lazy_compile. To restore the original
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    functionality, call reset_compile().
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    """
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    re.compile = lazy_compile
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def reset_compile():
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    """Restore the original function to re.compile().
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2063.4.2 by John Arbash Meinel
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    It is safe to call reset_compile() multiple times, it will always
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    restore re.compile() to the value that existed at import time.
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    Though the first call will reset back to the original (it doesn't
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    track nesting level)
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    """
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    re.compile = _real_re_compile
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_real_re_compile = re.compile
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if _real_re_compile is lazy_compile:
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    raise AssertionError(
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        "re.compile has already been overridden as lazy_compile, but this would" \
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        " cause infinite recursion")