26 - 语法 - def __xx__()魔法方法 - 需要自己定义

自定义方法汇总

__new__(cls[, ...])可用单例模式

class Dog():
    # 优先级1
    # 单例模式(只能创建一个)
    # 音乐播放 对象（同时播一首歌）
    # 回收站 对象（同时都扔到一个垃圾桶）
    # 打印机 对象（同时打一份）
    instance = None  # 记录第一个被创建对象的引用
    init_flag = False  # 记录是否执行过初始化动作
    def __new__(cls, *args, **kwargs):
        if cls.instance is None:  # 1. 判断类属性是否已经被赋值
            cls.instance = super().__new__(cls)
        return cls.instance # 2. 返回类属性的单例引用
        # 必须返回一个对象，否则不跑__new__()方法
    def __init__(self, name):
        self.name = name
if __name__ == "__main__":
    my_dog_1 = Dog('A')
    print(my_dog_1)
    my_dog_1.color = "yellow"
    print(my_dog_1.name)
    my_dog_2 = Dog('B')
    print(my_dog_2)
    print(my_dog_2.name)
    print(my_dog_2.color)  # 修改了my_dog_1，但是my_dog_2也被修改了

<__main__.Dog object at 0x7f95802d9a50>
A
<__main__.Dog object at 0x7f95802d9a50>
B
yellow

__init__(self[, ...])

class Dog():
    def __init__(self, name):
        self.name = name
if __name__ == "__main__":
    my_dog_1 = Dog('A')
    print(my_dog_1)
    print(my_dog_1.name)
    my_dog_2 = Dog('B')
    print(my_dog_2)  # 2个的内存空间不一样
    print(my_dog_2.name)

<__main__.Dog object at 0x7fb640219e50>
A
<__main__.Dog object at 0x7fb640219d90>
B

__del__(self)

class Dog():
    def __init__(self, name):
        self.name = name
    # 对象被删除（内存删除了）后会用
    # del my_dog
    # 出个告警？
    def __del__(self):
        print("__del__方法被调用")
if __name__ == "__main__":
    my_dog_1 = Dog('A')
    print(my_dog_1)
    print(my_dog_1.name)

<__main__.Dog object at 0x7fbf28219e90>
A
__del__方法被调用

__call__(self[, args...])

class Dog():
    def __init__(self, name):
        self.name = name
    # 可以让my_dog成为可调用对象
    # my_dog('W', 6)
    def __call__(self,age):
        self.age = age
        print("调用__call__()方法",age)
if __name__ == "__main__":
    my_dog_1 = Dog('A')
    my_dog_1(23)
    print(my_dog_1.age)

调用__call__()方法 23
23

__len__(self)长度

class Dog_1(object):
    def __init__(self, age):
        self.age = age
        self.li = ['a', 'v', 's']
class Dog(object):
    def __init__(self, age):
        self.age = age
        self.li = ['a', 'v', 's']
    def __len__(self):
        return len(self.li)
U = Dog(12)
print(len(U)) # 3
U = Dog_1(12)
print(len(U)) # 'Dog_1' has no len()

__contains__(self, item)是否包含

class Student():
    def __init__(self,name):
        self.name=name
    def __contains__(self,item):
        return item in self.name
s=Student("Jack")
print("J" in s)
## True