Bug overriding operators in new-style classes?

[Nicodemus]

Hi all,

I found a surprising behavior regarding new-style classes operator lookup.
It seems that for operators, the instance methods are ignored. Observe:

>>> class C:
...     def foo(self):
...         print 'foo'
...     def __setitem__(self, k, v):
...         print 'C.__setitem__', k, v
...
>>> c = C()
>>> c.foo()
foo
>>> c[1] = 1
C.__setitem__ 1 1
>>> def my_foo():
...     print 'my_foo'
...
>>> def my_setitem(k, v):
...     print 'my_setitem', k, v
...
>>> c.foo = my_foo
>>> c.__setitem__ = my_setitem
>>> c.foo()
my_foo
>>> c[1] = 1
my_setitem 1 1
>>>

All is well. Now, if you use a new-style class, the instance method is not
called:

>>> class C(object):
...     def foo(self):
...         print 'foo'
...     def __setitem__(self, k, v):
...         print 'C.__setitem__', k, v
...
>>> c = C()
>>> c.foo()
foo
>>> c[1] = 1
C.__setitem__ 1 1
>>> def my_foo():
...     print 'my_foo'
...
>>> def my_setitem(k, v):
...     print 'my_setitem', k, v
...
>>> c.foo = my_foo
>>> c.__setitem__ = my_setitem
>>> c.foo()
my_foo
>>> c[1] = 1
C.__setitem__ 1 1  # should print "my_setitem 1 1"
>>>

Is this a bug, or am I missing something? Any help would be appreciated.

Regards,
Nicodemus.