Python Errors when importing module from child directory

Question

I have a project that has this file structure:

f1
  f2
    __init__.py
    a.py
    b.py
  main.py

main.py

from f2 import a
...

a.py

import b
...

b.py

print('Hello World!')
...

When I run main.py, I get an import error from a.py saying "ImportError: No module named 'b'" but when I run a.py, it functions as expected.

f2 was initially a github submodule and the repo name had dashes. I thought that might have been the problem so I changed f2 to a directory and copied over the files. This has not solved my issue.

I have also tried using importlib.

I would expect that a.py is able to import b.py since it is able to when I run a.py directly.

Answer 1

That's because a thinks that b is a standalone module, so it looks for it in the PYTHONPATH directories, including the current folder.

However, when you run from main, b is no longer in the current folder (main's folder), and so a can't find it.

To solve this, change the import in a.py to from . import b, which signals that b.py is in the same package and to perform a relative import accordingly.