Module not found error with Python in Docker

Question

My directory structure:

    .
    |--app
    |   |--__init__.py
    |   |--main.py
    |  
    |
    |--Dockerfile
    |--requirements.txt

I can build this and run it fine. But when I add another.py file to my project, like this:

    .
    |--app
    |   |--__init__.py
    |   |--main.py
    |   |--handler.py
    |
    |--Dockerfile
    |--requirements.txt

and I try to import a function from handler.py in main.py, like this:

    # main.py
    from handler import someFunc

then main.py gives me a NoModuelFound error for handler.py

Can someone explain how to fix this (and maybe also explain why this error is happening)?

Answer 1

Print out your sys.path as one of the first things you do in your application, there's a good chance it's not set in such a way to get easy access to the stuff under app .

The Google guidelines (the ones we follow, and the ones that have gotten us out of the bad habit of fiddling around with PYTHONPATH ) have two rules applicable here.

• Use absolute imports; and
• Don't import anything less than a module.

That would involve importing (and using) as follows:

from app import handler
handler.someFunc()