Can't set attributes on instance of “object” class

Question

So, I was playing around with Python while answering this question, and I discovered that this is not valid:

o = object()
o.attr = \'hello\'

<

Answer 1

So, investigating my own question, I discovered this about the Python language: you can inherit from things like int, and you see the same behaviour:

>>> class MyInt(int):
       pass

>>> x = MyInt()
>>> print x
0
>>> x.hello = 4
>>> print x.hello
4
>>> x = x + 1
>>> print x
1
>>> print x.hello
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'int' object has no attribute 'hello'

I assume the error at the end is because the add function returns an int, so I'd have to override functions like __add__ and such in order to retain my custom attributes. But this all now makes sense to me (I think), when I think of "object" like "int".