I am unsure about when to fix versions vs using the most liberal specification that works. Of course, the django-related code does not really have tests... Since this library is reused in a couple of places. I think the end user of the library will notice if something is terribly wrong with the version of django that they are using.

Even better would be to run the tests with tox to test w/ many versions of django. The tastypie tests do that, for an example.