Why is __init__() always called after __new__()?

Question

I'm just trying to streamline one of my classes and have introduced some functionality in the same style as the flyweight design pattern.

However, I'm a bit confused as to why __init__ is always called after __new__. I wasn't expecting this. Can anyone tell me why this is happening and how I can implement this functionality otherwise? (Apart from putting the implementation into the __new__ which feels quite hacky.)

Here's an example:

class A(object):

    _dict = dict()

    def __new__(cls):

        if 'key' in A._dict:

            print "EXISTS"

            return A._dict['key']

        else:

            print "NEW"

            return super(A, cls).__new__(cls)

    def __init__(self):

        print "INIT"

        A._dict['key'] = self

        print ""

a1 = A()

a2 = A()

a3 = A()

Outputs:

NEW

INIT

EXISTS

INIT

EXISTS

INIT

Why?

Answer 1

Since the __new__ function is called when creating the instance and __init__ is called when initializing the instance and these two steps happen in this order only, so the __new__ function is always called first and __init__ function is called after that.