It isn't 'enforced' by Python at a language level, but as dmoisset stated, it makes the failure messages actually make sense:
"Expected 'foo', got 'bar'". (paraphrasing failure message: don't have any failing tests to look at right now. YAY! :) Matt. > -- You received this message because you are subscribed to the Google Groups "Django developers" group. To view this discussion on the web visit https://groups.google.com/d/msg/django-developers/-/3B4s7zenKmIJ. To post to this group, send email to django-developers@googlegroups.com. To unsubscribe from this group, send email to django-developers+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-developers?hl=en.