What role do __init___ and self play?

I'll explain it with the following code

class A(object):
    def __init__(self):
        self.x = 'Hello'

    def method_a(self, foo):
        print self.x + ' ' + foo

a = A()

self means an instance of the object itself. Object-oriented language most of this method to deliver, but you can't see it. Defines a method of the class from the Python when self the and clear. when the methods to retrieve any self is automatically delivered.

__init__ is the constructor used by Python.

In the above code, A() is It does not hand over any parameters to the constructor _init__ and generates an object of type A as a result and returns it.

If you write A (24, 'Hello'), you need a constructor that receives two parameters Currently, __init__ does not accept any parameters, so an exception occurs.