Why do we need __init__ to initialize a python class

Question

I'm pretty new to OOP and I need some help understanding the need for a constructor in a python class.

I understand init is used to initialize class variables like below:

class myClass():
    def __init__ (self):
        self.x = 3
        print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)

Output:

object created
3
6

but, I could also just do,

class myClass():
    x = 3
    print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)

which prints out the same result.

Could you please explain why we need a constructor or give me an example of a case when the above method will not work?

Answer 1

Citation: But I can also do

class myClass():
    x = 3
    print("object created")

A = myClass()
print(A.x)
A.x = 6
print(A.x)

No you cannot. There is a fundamental difference once you want to create two or more objects of the same class. Maybe this behaviour becomes clearer like this

class MyClass:
    x = 3
    print("Created!")

a = MyClass() # Will output "Created!"
a = MyClass() # Will output nothing since the class already exists!

In principle you need __init__ in order to write that code that needs to get executed for every new object whenever this object gets initialized / created - not just once when the class is read in.

Answer 2

__init__用于初始化类的多个实例的状态，其中每个实例的状态彼此分离，而您的第二个示例，没有__init__初始化在类的所有实例之间共享的属性。

Answer 3

init () is a default method which is called every time an object is created,so here the variables inside the init are called as instance attributes. the init () is called automatically every time an object is created, data you pass to object when it is created it gets assigned to the instance variables with the init () method here we are simply binding the method and the variables, and each object will have separate copy of these instance variables changing the data in one object will not effect it in another object