单例模式python

装饰器

def Singleton(func):
    _instance = {}

    def _singleton(*args, **kargs):
        if func not in _instance:
            _instance[func] = func(*args, **kargs)
        return _instance[func]

    return _singleton


@Singleton
class A(object):
    a = 1

    def __init__(self, x=0):
        self.x = x


a1 = A(2)
a2 = A(3)
print(id(a1))
print(id(a2))

基于__new__方法实现

class Singleton:
    instance = {}
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, "instance"):
            cls.instance = super().__new__()
        return cls.instance


class Foo(Singleton):
    pass

a = Foo()
b = Foo()
c = Foo()

print(id(a))
print(id(b))
print(id(c))