You're probably thinking of jsobject¹:

    from jsobject import Object
    foo = Object()
    foo.x = 1
    foo.a = {}  # foo.a.b will fail without this line
    foo.a.b = 2
    print(foo)  # prints: {'a': {'b': 2}, 'x': 1}

¹ https://pypi.python.org/pypi/jsobject/