What is the difference writing code in a class and in def __init__(self) in Python? [duplicate]

Answer 1

Let us consider the following class definition:

class Main:
        x = 1

        def __init__(self):
            self.y = 5

In this case, we can refer x directly like: Main.x i.e. it is a class attribute, this belongs to every objects of this class.

>>>Main.x
1

But, attribute y is specific to each object. We can not refer it directly like this:

>>> Main.y
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: class Main has no attribute 'y'

You need to instantiate an object of the class Main to refer to y:

>>> obj = Main()
>>> obj.y
5

This is similar to static variables in C++ and Java.