A fellow developer on a project I am on believes that doctests are as good as unit-tests, and that if a piece of code is doctested, it does not need to be unit-tested. I do not believe this to be the case. Can anyone provide some solid, ideally cited, examples either for or against the argument that doctests replace the need for unit-tests?
Thank you
-Daniel
EDIT: Can anyone provide a reference showing that doctesting should not replace unit-testing?
doctests are great for some uses

working and up to date documentation
sample tests embeded in docstrings
spikes or design phases when classes API is not really clear

unit tests are better in differents cases:

when you need clear and somewhat complex setup/teardown
when trying to get better coverage of all cases, inclusinf corner cases
for keeping tests independant from each other

In other words, at least for my own use, doctests are great when you focus on explaining what you are doing (docs, but also design phases) but more of a burden when you intent to use tests as a seat belt for refactoring or code coverage.
Does Python doctest remove the need for unit-tests?