常见设计模式 Python 实现

class op(object):
    def get_ans(self):
        pass

class Add(op):
    def get_ans(self):
        return self.a + self.b

class Mul(op):
    def get_ans(self):
        return self.a * self.b

class Undef(op):
    def get_ans(self):
        return "UNDEF!"

class Factory(op):
    operator = dict()
    operator["+"] = Add()
    operator["*"] = Mul()
    def create_operator(self, ch):
        t = self.operator[ch] if ch in self.operator else Undef()
        return t

if __name__ == "__main__":
    a = int(input())
    b = int(input())
    op = input()
    factory = Factory()
    cal = factory.create_operator(op)
    cal.a = a
    cal.b = b
    print(cal.get_ans())

class Singleton:
    class __My_class:
        def __init__(self, arg):
            self.arg = arg

        def show(self):
            return (id(self), self.arg)

    _instance = None
    def __init__(self, arg):
        if not Singleton._instance:
            Singleton._instance = Singleton.__My_class(arg)
        else:
            Singleton._instance.arg = arg
    def __getattr__(self, attr):
        return getattr(self._instance, attr)

if __name__ == "__main__":
    s1 = Singleton("bar")
    s2 = Singleton("zoo")
    print(s1.show())
    print(s2.show())