Python - why use “self” in a class?

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

Just as a side note: self is actually just a randomly chosen word, that everyone uses, but you could also use this, foo, or myself or anything else you want, it's just the first parameter of every non static method for a class. This means that the word self is not a language construct but just a name:

>>> class A:
...     def __init__(s):
...        s.bla = 2
... 
>>> 
>>> a = A()
>>> a.bla
2