Python设计模式----3.单例模式

单例模式：主要目的是确保某一个类只有一个实例存在

代码：

class A():
    def __new__(self, *args, **kwargs):
        if not hasattr(self, 'name'):
            testname = super(A, self)
            self.name = testname.__new__(self)
        return self.name

class B1(A):
    def __init__(self, name):
        self.name = name

class B2(A):
    def __init__(self, name):
        self.name = name 

a = B1('zhangsan')
print(a.name)          # zhangsan

b = B1('lisi')
c = B2('wangwu')
print(b.name)          # lisi
print(c.name)          # wangwu

b.name = 'zhaoliu'
print(a.name)          # zhaoliu
print(b.name)          # zhaoliu

结果：