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diff --git a/bzrlib/lazy_regex.py b/bzrlib/lazy_regex.py
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+# Copyright (C) 2006 Canonical Ltd
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+"""Lazily compiled regex objects.
+
+This module defines a class which creates proxy objects for regex
+compilation.  This allows overriding re.compile() to return lazily compiled
+objects.  
+
+We do this rather than just providing a new interface so that it will also
+be used by existing Python modules that create regexs.
+"""
+
+from __future__ import absolute_import
+
+import re
+
+from bzrlib import errors
+
+
+class LazyRegex(object):
+    """A proxy around a real regex, which won't be compiled until accessed."""
+
+
+    # These are the parameters on a real _sre.SRE_Pattern object, which we
+    # will map to local members so that we don't have the proxy overhead.
+    _regex_attributes_to_copy = [
+                 '__copy__', '__deepcopy__', 'findall', 'finditer', 'match',
+                 'scanner', 'search', 'split', 'sub', 'subn'
+                 ]
+
+    # We use slots to keep the overhead low. But we need a slot entry for
+    # all of the attributes we will copy
+    __slots__ = ['_real_regex', '_regex_args', '_regex_kwargs',
+                ] + _regex_attributes_to_copy
+
+    def __init__(self, args=(), kwargs={}):
+        """Create a new proxy object, passing in the args to pass to re.compile
+
+        :param args: The `*args` to pass to re.compile
+        :param kwargs: The `**kwargs` to pass to re.compile
+        """
+        self._real_regex = None
+        self._regex_args = args
+        self._regex_kwargs = kwargs
+
+    def _compile_and_collapse(self):
+        """Actually compile the requested regex"""
+        self._real_regex = self._real_re_compile(*self._regex_args,
+                                                 **self._regex_kwargs)
+        for attr in self._regex_attributes_to_copy:
+            setattr(self, attr, getattr(self._real_regex, attr))
+
+    def _real_re_compile(self, *args, **kwargs):
+        """Thunk over to the original re.compile"""
+        try:
+            return _real_re_compile(*args, **kwargs)
+        except re.error, e:
+            # raise InvalidPattern instead of re.error as this gives a
+            # cleaner message to the user.
+            raise errors.InvalidPattern('"' + args[0] + '" ' +str(e))
+
+    def __getstate__(self):
+        """Return the state to use when pickling."""
+        return {
+            "args": self._regex_args,
+            "kwargs": self._regex_kwargs,
+            }
+
+    def __setstate__(self, dict):
+        """Restore from a pickled state."""
+        self._real_regex = None
+        setattr(self, "_regex_args", dict["args"])
+        setattr(self, "_regex_kwargs", dict["kwargs"])
+
+    def __getattr__(self, attr):
+        """Return a member from the proxied regex object.
+
+        If the regex hasn't been compiled yet, compile it
+        """
+        if self._real_regex is None:
+            self._compile_and_collapse()
+        # Once we have compiled, the only time we should come here
+        # is actually if the attribute is missing.
+        return getattr(self._real_regex, attr)
+
+
+def lazy_compile(*args, **kwargs):
+    """Create a proxy object which will compile the regex on demand.
+
+    :return: a LazyRegex proxy object.
+    """
+    return LazyRegex(args, kwargs)
+
+
+def install_lazy_compile():
+    """Make lazy_compile the default compile mode for regex compilation.
+
+    This overrides re.compile with lazy_compile. To restore the original
+    functionality, call reset_compile().
+    """
+    re.compile = lazy_compile
+
+
+def reset_compile():
+    """Restore the original function to re.compile().
+
+    It is safe to call reset_compile() multiple times, it will always
+    restore re.compile() to the value that existed at import time.
+    Though the first call will reset back to the original (it doesn't
+    track nesting level)
+    """
+    re.compile = _real_re_compile
+
+
+_real_re_compile = re.compile
+if _real_re_compile is lazy_compile:
+    raise AssertionError(
+        "re.compile has already been overridden as lazy_compile, but this would" \
+        " cause infinite recursion")