/usr/lib/python3/dist-packages/openpyxl/compat/singleton.py is in python3-openpyxl 2.4.9-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | from __future__ import absolute_import
# Copyright (c) 2010-2017 openpyxl
import weakref
class Singleton(type):
"""
Singleton metaclass
Based on Python Cookbook 3rd Edition Recipe 9.13
Only one instance of a class can exist. Does not work with __slots__
"""
def __init__(self, *args, **kw):
super(Singleton, self).__init__(*args, **kw)
self.__instance = None
def __call__(self, *args, **kw):
if self.__instance is None:
self.__instance = super(Singleton, self).__call__(*args, **kw)
return self.__instance
class Cached(type):
"""
Caching metaclass
Child classes will only create new instances of themselves if
one doesn't already exist. Does not work with __slots__
"""
def __init__(self, *args, **kw):
super(Singleton, self).__init__(*args, **kw)
self.__cache = weakref.WeakValueDictionary()
def __call__(self, *args):
if args in self.__cache:
return self.__cache[args]
obj = super(Singleton, self).__call__(*args)
self.__cache[args] = obj
return obj
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