Circular import dependency in Python

I've wondered this a couple times (usually while dealing with models that need to know about each other). The simple solution is just to import the whole module, then reference the thing that you need.

So instead of doing

from models import Student

in one, and

from models import Classroom

in the other, just do

import models

in one of them, then call models.Classroom when you need it.

If a depends on c and c depends on a, aren't they actually the same unit then?

You should really examine why you have split a and c into two packages, because either you have some code you should split off into another package (to make them both depend on that new package, but not each other), or you should merge them into one package.

You may defer the import, for example in a/__init__.py:

def my_function():
    from a.b.c import Blah
    return Blah()

that is, defer the import until it is really needed. However, I would also have a close look at my package definitions/uses, as a cyclic dependency like the one pointed out might indicate a design problem.