Django way for dynamic forms with dependencies?

I'm looking for a django way to handle some complex forms with a lot of business logic. The issue is many of my forms have dependencies in them.
Some examples:
1. two "select" (choice) fields that are dependent on each other. For example consider two dropdowns one for Country and one for City.
2. A "required-if" rule, i.e set field required if something else in the form was selected. Say if the user select "Other" option in a select field, he need to add an explanation in a textarea.
3. Some way to handle date/datetime fields, i.e rules like max/min date?

What I'm doing now is implementing all of these in the form clean(), __init__(), and write some (tedious) client-side JS.

I wonder if there is a better approach? like defining these rules in a something similar to django Meta classes.