Python使用metaclass实现Singleton模式的方法

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()

Singleton newSingleton initSingleton callCache newCache init<__main__.Cache object at 0x01CDB130>Singleton call<__main__.Cache object at 0x01CDB130>