View file File name : descriptors.py Content :# 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: """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 def __delete__(self, obj): self.instances[obj] = None