How to make python class support item assignment?

In Python 3 and later, just add these simple functions to your class:

class some_class(object):
    def __setitem__(self, key, value):
        setattr(self, key, value)

    def __getitem__(self, key):
        return getattr(self, key)

They are accomplishing this magic by inheriting from dict. A better way of doing this is to inherit from UserDict or the newer collections.MutableMapping

You could accomplish a similar result by doing the same:

import collections

class ObjectChild(collections.MutableMapping):
    def __init__(self, name):
        self['name'] = name

You can also define two special functions to make your class dictionary-like: __getitem__(self, key) and __setitem__(self, key, value). You can see an example of this at Dive Into Python - Special Class Methods.

Disclaimer : I might be wrong.

the notation :

self[something]

is legit in the Graph class because it inherits fro dict. This notation is from the dictionnaries ssyntax not from the class attribute declaration syntax.

Although all namespaces associated with a class are dictionnaries, in your class ChildObject, self isn't a dictionnary. Therefore you can't use that syntax.

Otoh, in your class Graph, self IS a dictionnary, since it is a graph, and all graphs are dictionnaries because they inherit from dict.