Out of curiosity, how long does it usually take people to answer the second question? I'm talking about good candidates, not people who don't code.
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".
Anonymous functions in Python are what immediately popped into my mind. I do embedded work and mostly use C, but a lot of the problems with C actually make since when you have less than 1 kB of RAM. I'd prefer to use Lua for building test applications and the like, but I keep going back to Python because the library support is tremendous in comparison.
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 use Python mostly, and I was asked this in an interview question (shortly after being asked if I could enumerate the differences between 2.6 and 3, when I said 'quite frankly no, I'm building a real world app and focused entirely on 2.6 at the moment since migrating to 3 isn't an option').
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.
Python has it's share of warts. Its automatic memory management is not a modern GC, it involves reference counters that are slow, take up memory and don't play well with copy-on-write semantics of modern virtual memory managers. Its functional programming support is half-hearthed, its implementation is slow, there is no optional static typing, the GIL sucks. And yet it's the best programming language for me - the others are worse.
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".