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##
# Copyright (c) 2011-2015 Apple Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
##
"""
A small utility for defining static class properties.
"""
__all__ = ["classproperty"]
class classproperty(object):
"""
Decorator for a method that wants to return a static class property. The
decorated method will only be invoked once, for each class, and that value
will be returned for that class.
"""
def __init__(self, thunk=None, cache=True):
self.cache = cache
self.thunk = thunk
self._classcache = {}
def __call__(self, thunk):
return self.__class__(thunk, self.cache)
def __get__(self, instance, owner):
if not self.cache:
return self.thunk(owner)
cc = self._classcache
if owner in cc:
cached = cc[owner]
else:
cached = self.thunk(owner)
cc[owner] = cached
return cached
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