Python中使用 metaclass 实现Singleton 模式

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class Singleton(type):     def __call__(cls, *args, **kwargs):         print "Singleton call"         if not hasattr(cls, 'instance'):             cls.instance = super(Singleton, cls).__call__(*args, **kwargs)         return cls.instance     def __new__(cls, name, bases, dct):         print "Singleton new"         return type.__new__(cls, name, bases, dct)       def __init__(cls, name, bases, dct):         print "Singleton init"         super(Singleton, cls).__init__(name, bases, dct)   class Cache(object):     __metaclass__ = Singleton     def __new__(cls, *args, **kwargs):         print "Cache new"         return object.__new__(cls, *args, **kwargs)     def __init__(cls, *args, **kwargs):         print "Cache init"     def __call__(cls, *args, **kwargs):         print "Cache call"   print Cache() print Cache()

 

 输出：

Singleton new
Singleton init
Singleton call
Cache new
Cache init
<__main__.Cache object at 0x01CDB130>
Singleton call
<__main__.Cache object at 0x01CDB130>