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# Copyright 2015, Tresys Technology, LLC
#
# This file is part of SETools.
#
# SETools is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as
# published by the Free Software Foundation, either version 2.1 of
# the License, or (at your option) any later version.
#
# SETools 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with SETools. If not, see
# <http://www.gnu.org/licenses/>.
#
from weakref import WeakKeyDictionary
class DiffResultDescriptor(object):
"""Descriptor for managing diff results."""
# @properties could be used instead, but there are so
# many result attributes, this will keep the code cleaner.
def __init__(self, diff_function):
self.diff_function = diff_function
# use weak references so instances can be
# garbage collected, rather than unnecessarily
# kept around due to this descriptor.
self.instances = WeakKeyDictionary()
def __get__(self, obj, objtype=None):
if obj is None:
return self
if self.instances.setdefault(obj, None) is None:
diff = getattr(obj, self.diff_function)
diff()
return self.instances[obj]
def __set__(self, obj, value):
self.instances[obj] = value
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