dependencies - Circular import dependency in Python

Question

Let's say I have the following directory structure:

a
    __init__.py
    b
        __init__.py
        c
            __init__.py
            c_file.py
        d
            __init__.py
            d_file.py

In the a package's __init__.py, the c package is imported. But c_file.py imports a.b.d.

The program fails, saying b doesn't exist when c_file.py tries to import a.b.d. (And it really doesn't exist, because we were in the middle of importing it.)

How can this problem be remedied?

Answer 1

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.