AttributeError when using object.__setattr__

Question

What's wrong with the last three lines?

class FooClass(object):
    pass 
bar1 = object() 
bar2 = object() 
bar3 = object() 
foo1 = FooClass() 
foo2 = FooClass() 
foo3 = FooClass() 
object.__setattr__(foo1,'attribute','Hi')
foo2.__setattr__('attribute','Hi')
foo3.attribute = 'Hi'
object.__setattr__(bar1,'attribute','Hi')
bar2.attribute = 'Hi'
bar3.attribute = 'Hi'

I need an object having a single attribute (like foo) should I define a class (like FooClass) just for it?

Answer 1

object is built-in type, so you can't override attributes and methods of its instances.

Maybe you just want a dictionary or collections.NamedTuples:

>>> d = dict(foo=42)
{'foo': 42}
>>> d["foo"]
42

>>> from collections import namedtuple
>>> Point = namedtuple('Point', ['x', 'y'], verbose=True)
>>> p = Point(11, y=22)     # instantiate with positional or keyword arguments
>>> p[0] + p[1]             # indexable like the plain tuple (11, 22) 33
>>> x, y = p                # unpack like a regular tuple
>>> x, y (11, 22)
>>> p.x + p.y               # fields also accessible by name 33
>>> p                       # readable __repr__ with a name=value style Point(x=11, y=22)

Answer 2

You cannot add new attributes to an object(), only to subclasses.

Try collections.NamedTuples.

Besides, instead of object.__setattr__(foo1,'attribute','Hi'), setattr(foo1, 'attribute', 'Hi') would be better.