I'm asking because I've actually seen this question mentioned before, and each time, I spend some time thinking about it (as applied to Python). But it honestly takes me some time to think of problems with Python; not because it's perfect, just because I don't spend every day thinking "hey why can't it do this".
If you use multiple languages regularly surely there are some things in each language which you think is better in the other ones?
In any event, I think the question of what problems you have with your favorite language is at least a good conversation starter. It would be nice to know that those kinds of conversations are easy and interesting to a candidate. Although, that isn't necessarily a requirement.
I was actually working closely with Django so ended up listing things I disliked about Django rather than Python itself. I think one of the easier ways to answer would've been with a Javascript/C/ML/Lisp hat on - was chatting to someone at the weekend who was totally against the space-indentation, for example.