Class initialization and callback usage

Learning goals ：

Distinguish correctly Class initialization and callback

About class initialization

class A():
    def __init__(self):
        print('Hello, world！')
A()

Calls to classes

class A():
    def __call__(self):
        print('hello,world!!!!!!!!!!!!!!')
a = A()
a()

 This is it. __init__ And __call__ The difference in usage ！

About their specific application in programming

Example 1

class A():
    def __init__(self):
        print('hello,world!')

    def __call__(self):
        print('hello,world!!!!!!!!!!!!!')
a = A()
a()

Example 2

class A():
    def __init__(self, init_age):
        print(' My age is :', init_age)
        self.age = init_age
    def __call__(self, added_age):
        res = self.forward(added_age)  # call forward function 
        return res
    def forward(self, input_):
        print('forward  Function called ')
        return input_ + self.age
print(' Object initialization ………………')
a = A(16)
input_param = a(2)
print(" My age now will always be ：", input_param)

Example 3

class Animal():
    def __init__(self,name):
        self.name = name
    def greet(self):
        print('animal is {}'.format(self.name))
class Cat(Animal):
    def greet(self):
        super(Cat, self).greet()
        print("It's name is wangwang")
a=Cat('cat')
a.greet()

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