The question is quite clear, ... note however that I am NOT asking about a feature comparison (there are a lot of them already), nor am I asking about which one you prefer !
I have myself a clear preference for doctests, I use them for everything, even if those are not to be used for documentation. But what I am wondering is : is there anything you can do with unitests that you cannot do with doctests ???
Doctests are limited to per function (or per class) tests. You cannot do things like taking the output of one function and trying it with another etc. It's best used for "example" type tests (i.e. how do I use this function?)
Unit tests can be larger and more involved than doctests.
Python: Does 'unittest' have something that 'doctest' hasn't?