> Well this is what I get:
> 
> $ python3
> Python 3.4.0a1+ (default:41de6f0e62fd+, Aug 27 2013, 18:44:07)
> [GCC 4.2.1 Compatible Apple LLVM 4.2 (clang-425.0.28)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
> >>> from collections import namedtuple
> from collections import namedtuple
> >>> A = namedtuple('A', 'foo bar')
> A = namedtuple('A', 'foo bar')
> >>> class B(A):
> class B(A):
> ...   __slots__ = ['baz']
>   __slots__ = ['baz']
> ... 
> 
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: nonempty __slots__ not supported for subtype of 'A'

Ah, ok, you're right. I only use empty __slots__ :-)