| 12345678910111213141516171819202122232425262728293031323334353637383940 |
- # Copyright (c) 2010-2024 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().__init__(*args, **kw)
- self.__instance = None
- def __call__(self, *args, **kw):
- if self.__instance is None:
- self.__instance = super().__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().__init__(*args, **kw)
- self.__cache = weakref.WeakValueDictionary()
- def __call__(self, *args):
- if args in self.__cache:
- return self.__cache[args]
- obj = super().__call__(*args)
- self.__cache[args] = obj
- return obj
|
