blob: dc844a53ab2d8dc33ed51b3f06691668e737f0ae [file] [log] [blame]
eric@webkit.org8baf0e92010-10-28 05:12:39 +00001# Copyright (c) 2010 Google Inc. All rights reserved.
2#
3# Redistribution and use in source and binary forms, with or without
4# modification, are permitted provided that the following conditions are
5# met:
6#
7# * Redistributions of source code must retain the above copyright
8# notice, this list of conditions and the following disclaimer.
9# * Redistributions in binary form must reproduce the above
10# copyright notice, this list of conditions and the following disclaimer
11# in the documentation and/or other materials provided with the
12# distribution.
13# * Neither the name of Google Inc. nor the names of its
14# contributors may be used to endorse or promote products derived from
15# this software without specific prior written permission.
16#
17# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
18# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
19# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
20# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
21# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
22# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
23# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
27# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28
29# Python does not (yet) seem to provide automatic memoization. So we've
30# written a small decorator to do so.
31
32import functools
33
34
35class memoized(object):
36 def __init__(self, function):
37 self._function = function
38 self._results_cache = {}
39
40 def __call__(self, *args):
41 try:
42 return self._results_cache[args]
43 except KeyError:
44 # If we didn't find the args in our cache, call and save the results.
45 result = self._function(*args)
46 self._results_cache[args] = result
47 return result
48 # FIXME: We may need to handle TypeError here in the case
49 # that "args" is not a valid dictionary key.
50
51 # Use python "descriptor" protocol __get__ to appear
52 # invisible during property access.
53 def __get__(self, instance, owner):
54 # Return a function partial with obj already bound as self.
55 return functools.partial(self.__call__, instance)