Function singleton

Target Offer/Singleton.py:65–71

(cls, *args, **kwargs)

单例类本身根本不知道自己是单例的，因为他自己的代码并不是单例的
'''
def singleton(cls, *args, **kwargs):
    instances = {}
    def getinstance():
        if cls not in instances:
            instances[cls] = cls(*args, **kwargs)
        return instances[cls]
    return getinstance
@singleton
class MyClass3(object):
    a = 1