Python用元类实现缓存实例

import weakref


class Cached(type):

    def __init__(cls, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # weakref 不影响GC
        # 缓存中常用 weakref
        cls._cache = weakref.WeakValueDictionary()

    def __call__(cls, *args):
        # tuple 作为 key
        if args in cls._cache:
            return cls._cache[args]
        else:
            # 此处对调用 Logger类中的 __new__ __init__ 方法
            obj = super().__call__(*args)
            cls._cache[args] = obj
            return obj


class CachedBase(metaclass=Cached):
    pass


class Logger(CachedBase):
    # Logger() 首先会走到元类的 __call__ 方法
    def __init__(self, name):
        self.name = name


if __name__ == '__main__':
    l1 = Logger('l1')
    l2 = Logger('l2')
    l3 = Logger('l1')

    print(l1 is l2)
    print(l1 is l3)