Question

How do these 2 classes differ?

class A():     x=3  class B():     def __init__(self):         self.x=3 

Is there any significant difference?

Answer 1

A.x is a class variable. B‘s self.x is an instance variable.

i.e. A‘s x is shared between instances.

It would be easier to demonstrate the difference with something that can be modified like a list:

#!/usr/bin/env python  class A:     x = []     def add(self):         self.x.append(1)  class B:     def __init__(self):         self.x = []     def add(self):         self.x.append(1)  x = A() y = A() x.add() y.add() print('A's x:', x.x)  x = B() y = B() x.add() y.add() print('B's x:', x.x) 

Output

A's x: [1, 1] B's x: [1]