why new-style classes?

classes.py

>>> class NewStyle(object):
...     def foo(self):
...         return 'foo'

>>> class OldStyle():
...     def foo(self):
...         return 'foo'

>>> dir(NewStyle)
['__class__',
 '__delattr__',
 '__dict__',
 '__doc__',
 '__format__',
 '__getattribute__',
 '__hash__',
 '__init__',
 '__module__',
 '__new__',
 '__reduce__',
 '__reduce_ex__',
 '__repr__',
 '__setattr__',
 '__sizeof__',
 '__str__',
 '__subclasshook__',
 '__weakref__',
 'foo']

>>> dir(OldStyle)
['__doc__', '__module__', 'foo']

>>> n = NewStyle()

>>> o = OldStyle()

>>> type(n)
__main__.NewStyle

>>> type(o)
instance

>>> class OldChild(OldStyle):
...     def foo(self):
...         return super(OldChild, self).foo() + 'bar'

>>> oc = OldChild()

>>> oc.foo()
TypeError: must be type, not classobj

http://stackoverflow.com/a/19950198/29654