class Singleton(object):
def __new__(cls, *args, **kwargs):
if not hasattr(cls, '_instance'):
cls._instance = super(Singleton, cls).__new__(cls)
return cls._instance
注：__new__方法用于生成类实例，__new__应返回一个类实例，返回值会传到__init__方法用于生成实例，对应着__init__方法中的"self"参数。