With doctest.ELLIPSIS, you can use ... to mean “match any string here”. You can set doctest options with a doctest directive, to make it active for just one test case: one example in the online docs is:
>>> print range(20) # doctest:+ELLIPSIS
[0, 1, ..., 18, 19]
If you want a doctest option to be active throughout, you can pass it as the optionflags= argument to whatever doctest functions you use, e.g. doctest.testfile. (You can pass multiple option flags there by using the | operator to bit-or them).