Python-Python实现单例模式

面试官问我， 听说过单例模式吗，我说听说过， 然后说让我写下Python的单例模式。然后我就懵逼了。 之前看过， 因为没有记录， 忘的嘎嘣脆。。。

Python中一切皆对象。

最简单的单例模式

class Class_A(object):
    print("single_model")
    
def single_instance():
    return Class_A

print(id(single_instance()))
print(id(single_instance()))

single_model
94873513761768
94873513761768

正规的单例模式

class Singleton(object):
    _instance = None
    def __new__(self, *args, **kwargs):
        if self._instance is None:
            self._instance = object.__new__(self, *args, **kwargs)

        return self._instance

s1 = Singleton()
s2 = Singleton()
print(id(s1))
print(id(s2))

139693198402056
139693198402056

工厂模式

class Fruit(object):
    def __init__(self):
        pass

    def print_color(self):
        print("I do not know!")

class Apple(Fruit):
    def __init__(self):
        pass

    def print_color(self):
        print("apple is in red")

class Orange(Fruit):
    def __init__(self):
        pass

    def print_color(self):
        print("orange is in orange")

class FruitFactory(object):
    fruits = {"apple": Apple, "orange": Orange}

    def __new__(self, name):
        if name in self.fruits.keys():
            print(name)
            return self.fruits[name]()
        else:
            return Fruit()
        
fruit1 = FruitFactory("apple")
fruit2 = FruitFactory("orange")
fruit3 = FruitFactory("fruit")

fruit1.print_color()    
fruit2.print_color()    
fruit3.print_color()    

apple
orange
apple is in red
orange is in orange
I do not know!

总结， 一直一来都没有好好总结用过的知识， 结果现在忘性越来越大，以后要保持每天一篇文章。（水也要水一篇）