Python 使用装饰器实现单例模式

def singleton(cls):
    instances = {}
    def getinstance(*args,**kwargs):
        if cls not in instances:
            instances[cls] = cls(*args,**kwargs)
        return instances[cls]
    return getinstance

@singleton
class MyClass:
    a = 1

c1 = MyClass()
c2 = MyClass()
print(c1 == c2) # True

定义一个@singleton装饰器，内部函数getinstance会判断类是否在字典中