~bzr-pqm/bzr/bzr.dev

2052.3.4 by John Arbash Meinel
[merge] bzr.dev
1
# Copyright (C) 2006 Canonical Ltd
2063.4.1 by John Arbash Meinel
bzrlib.lazy_regex.lazy_compile creates a proxy object around re.compile()
2
#
3
# This program is free software; you can redistribute it and/or modify
4
# it under the terms of the GNU General Public License as published by
5
# the Free Software Foundation; either version 2 of the License, or
6
# (at your option) any later version.
7
#
8
# This program is distributed in the hope that it will be useful,
9
# but WITHOUT ANY WARRANTY; without even the implied warranty of
10
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
11
# GNU General Public License for more details.
12
#
13
# You should have received a copy of the GNU General Public License
14
# along with this program; if not, write to the Free Software
15
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
16
17
"""Lazily compiled regex objects.
18
19
This module defines a class which creates proxy objects for regex compilation.
20
This allows overriding re.compile() to return lazily compiled objects.
21
"""
22
23
import re
24
25
26
class LazyRegex(object):
2063.4.5 by John Arbash Meinel
review feedback from Martin
27
    """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()
28
29
30
    # These are the parameters on a real _sre.SRE_Pattern object, which we
31
    # will map to local members so that we don't have the proxy overhead.
32
    _regex_attributes_to_copy = [
33
                 '__copy__', '__deepcopy__', 'findall', 'finditer', 'match',
34
                 'scanner', 'search', 'split', 'sub', 'subn'
35
                 ]
36
37
    # We use slots to keep the overhead low. But we need a slot entry for
38
    # all of the attributes we will copy
39
    __slots__ = ['_real_regex', '_regex_args', '_regex_kwargs',
40
                ] + _regex_attributes_to_copy
41
42
    def __init__(self, args=(), kwargs={}):
43
        """Create a new proxy object, passing in the args to pass to re.compile
44
45
        :param args: The *args to pass to re.compile
46
        :param kwargs: The **kwargs to pass to re.compile
47
        """
48
        self._real_regex = None
49
        self._regex_args = args
50
        self._regex_kwargs = kwargs
51
52
    def _compile_and_collapse(self):
53
        """Actually compile the requested regex"""
54
        self._real_regex = self._real_re_compile(*self._regex_args,
55
                                                 **self._regex_kwargs)
56
        for attr in self._regex_attributes_to_copy:
57
            setattr(self, attr, getattr(self._real_regex, attr))
58
59
    def _real_re_compile(self, *args, **kwargs):
60
        """Thunk over to the original re.compile"""
61
        return _real_re_compile(*args, **kwargs)
62
63
    def __getattr__(self, attr):
64
        """Return a member from the proxied regex object.
65
66
        If the regex hasn't been compiled yet, compile it
67
        """
68
        if self._real_regex is None:
69
            self._compile_and_collapse()
70
        # Once we have compiled, the only time we should come here
71
        # is actually if the attribute is missing.
72
        return getattr(self._real_regex, attr)
73
74
75
def lazy_compile(*args, **kwargs):
76
    """Create a proxy object which will compile the regex on demand.
77
78
    :return: a LazyRegex proxy object.
79
    """
80
    return LazyRegex(args, kwargs)
81
2063.4.2 by John Arbash Meinel
Add install and unistall functions, and tests
82
83
def install_lazy_compile():
84
    """Make lazy_compile the default compile mode for regex compilation.
85
86
    This overrides re.compile with lazy_compile. To restore the original
87
    functionality, call reset_compile().
88
    """
89
    re.compile = lazy_compile
90
91
92
def reset_compile():
93
    """Restore the original function to re.compile().
94
    
95
    It is safe to call reset_compile() multiple times, it will always
96
    restore re.compile() to the value that existed at import time.
97
    Though the first call will reset back to the original (it doesn't
98
    track nesting level)
99
    """
100
    re.compile = _real_re_compile
2063.4.5 by John Arbash Meinel
review feedback from Martin
101
102
103
_real_re_compile = re.compile
3376.2.4 by Martin Pool
Remove every assert statement from bzrlib!
104
if _real_re_compile is lazy_compile:
105
    raise AssertionError(
106
        "re.compile has already been overridden as lazy_compile, but this would" \
107
        " cause infinite recursion")