python魔术方法- __init__,_new_,_call_,_str_,_repr_,_add_,_getitem_,_getattr_,_bases_,_dict_，_slots_

# __new__ : 创建对象  Create and return a new object.
# __init__ : 初始化对象

class MyClass(object):
    def __init__(self):
        print("init is running ...")

    def __new__(cls, *args, **kwargs):
        # 创建对象
        # 分配内存
        print("new is running ...")
        obj = super().__new__(cls)  # 创建对象
        return obj

def add(x, y):
    return x + y

print(dir(add))

结果：
['__annotations__', '__call__', '__class__', '__closure__', '__code__', '__defaults__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__globals__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__kwdefaults__', '__le__', '__lt__', '__module__', '__name__', '__ne__', '__new__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']

class MyClass(object):
    def __init__(self, name):
        self.name = name

    def __str__(self):
        print("---str is running---")
        return self.name
        # return '1'


def main():
    obj = MyClass('马师傅')
    print(hasattr(obj, '__str__'))
    # 以下三种方式可以触发__str__
    print(obj) # return self.name返回 马师傅；return '1'返回 1
    str(obj)
    format(obj)


if __name__ == '__main__':
    main()


结果：
True
---str is running---
马师傅
---str is running---
---str is running---

class MyClass(object):
    def __init__(self, name):
        self.name = name

    # def __str__(self):
    #     print("---str is running---")
    #     return self.name
    #     # return '1'

    def __repr__(self):
        print("---repr is running---")
        return self.name
        # return '1'

def main():
    obj = MyClass('马师傅')
    print(hasattr(obj, '__str__'))
    # 以下三种方式可以触发__str__
    print(obj) # return self.name返回 马师傅；return '1'返回 1
    str(obj)
    format(obj)


if __name__ == '__main__':
    main()


结果：
True
---repr is running---
马师傅
---repr is running---
---repr is running---

class MyClass(object):

    def __init__(self, value):
        self.value = value

    def __add__(self, other):
        return self.value + other.value


def main():
    a = [1, 2]
    b = [3, 4]
    print(a + b)
    obj1 = MyClass(10.00)
    obj2 = MyClass(11.00)
    print(obj1 + obj2)
    print(hasattr(a, '__add__'))


if __name__ == '__main__':
    main()


结果：
[1, 2, 3, 4]
21.0
True

class MyClass(object):
    def __init__(self):
        self.items = ['a', 'b', 'c']

    # 有__getitem__方法的对象才能用[]操作
    def __getitem__(self, i):
        return self.items[i]


if __name__ == '__main__':
    obj = MyClass()
    print(obj[0])  # a
    print(obj[1])  # b
    print(obj[2])  # c
    print(hasattr(tuple, '__getitem__'))  # True
    print(hasattr(1, '__getitem__'))  # False
    print(hasattr(dict, '__getitem__'))  # True

    print({'name': 'xxx'}['name'])


结果：
a
b
c
True
False
True
xxx

class MyClass:

    def __init__(self,name):
        self.name = name

    # __getattr__ 当获得对象的属性，而对象无此属性时执行
    def __getattr__(self, item):
        return 999

myclass = MyClass("Tom")
print(myclass.name)
print(myclass.age)
        

结果：
Tom
999

class A(object):
    pass


class B(object):
    pass


class MyClass(A, B):
    pass


if __name__ == '__main__':
    print(MyClass.__bases__)

# __bases__: 就是一个元组，里面是继承的类

结果：
(<class '__main__.A'>, <class '__main__.B'>)

class MyClass(object):  # MyClass 是类 ， 类 其实就是 定义如何创建对象的一段代码
    a = 0  # 类变量 （归属于类）

    def __init__(self, name, age):
        temp = 1  # 局部变量
        self.name = name  # self  是对象
        self.age = age  # name ，age  实例变量（归属于对象）

    def get_name(self):
        return self.name


if __name__ == '__main__':
    obj = MyClass('Tom', 100)
    print(MyClass.__dict__)
    print(obj.__dict__)


结果：
{'__module__': '__main__', 'a': 0, '__init__': <function MyClass.__init__ at 0x00000213456FF940>, 'get_name': <function MyClass.get_name at 0x00000213456FFC10>, '__dict__': <attribute '__dict__' of 'MyClass' objects>, '__weakref__': <attribute '__weakref__' of 'MyClass' objects>, '__doc__': None}
{'name': 'Tom', 'age': 100}