Usefulness of def __init__(self)?

Question

I am fairly new to python, and noticed these posts: Python __init__ and self what do they do? and Python Classes without using def __init__(self)

After playing around w

Answer 1

In the first exemple you have the variable of the instance of the class. This variable is only accessible through an instance (self required).

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

print A.x -> AttributeError
print A().x -> 'hello'

In the second exemple you have a static variable. You can access to this variable thanks to the name of the class A

class A():
  x = 'hello'

print A.x -> 'hello'
print A().x -> 'hello'

In fact you can have a static variable and an instance variable with the same name:

class A():
    x = 'hello'
    def __init__(self):
        self.x = 'world'

print A.x -> hello
print A().x -> world

The static value is shared between all the instances

class A():
    x = 'hello'

    @staticmethod
    def talk():
        print A.x

a = A()
print a.talk() -> hello

A.x = 'world'
print a.talk() -> world

You have a good article here: http://linuxwell.com/2011/07/21/static-variables-and-methods-in-python/