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40 lines
1.1 KiB
40 lines
1.1 KiB
# Copyright (c) 2010-2022 openpyxl
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import weakref
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class Singleton(type):
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"""
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Singleton metaclass
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Based on Python Cookbook 3rd Edition Recipe 9.13
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Only one instance of a class can exist. Does not work with __slots__
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"""
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def __init__(self, *args, **kw):
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super(Singleton, self).__init__(*args, **kw)
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self.__instance = None
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def __call__(self, *args, **kw):
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if self.__instance is None:
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self.__instance = super(Singleton, self).__call__(*args, **kw)
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return self.__instance
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class Cached(type):
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"""
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Caching metaclass
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Child classes will only create new instances of themselves if
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one doesn't already exist. Does not work with __slots__
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"""
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def __init__(self, *args, **kw):
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super(Singleton, self).__init__(*args, **kw)
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self.__cache = weakref.WeakValueDictionary()
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def __call__(self, *args):
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if args in self.__cache:
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return self.__cache[args]
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obj = super(Singleton, self).__call__(*args)
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self.__cache[args] = obj
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return obj
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