ModuleNotFoundError: No module named in python 3 even after hacking sys.path()

Question

I have this file structure:

/home/test
         ├── dirA
         │   └── ClassA.py
         └── dirB
             └── Main.py

With the following content in the files:

ClassA.py:

class ClassA:
    def __str__(self):
        return 'Hi'

Main.py:

from dirA.ClassA import ClassA

class Main:

    def main():
        a = ClassA()

if __name__ == '__main__':
    Main.main()

I change the current dir to:

$ cd /home/test/dirB

This works:

$ PYTHONPATH=/home/test python Main.py

This doesn't:

$ python Main.py

Traceback (most recent call last):
  File "Main.py", line 1, in <module>
    from dirA.ClassA import ClassA
ModuleNotFoundError: No module named 'dirA'

Adding this lines in Main.py has no effect:

import os, sys
# Get the top level dir.
path = os.path.dirname(os.path.dirname(__file__)) 
sys.path.append(path)

The module still can't be found! There are plenty of similar questions but I couldn't make this work programmatically (skipping the PYTHONPATH env var.) I understand that dirs are not modules, files are but this works in PyCharm (is the IDE fixing PYTHONPATH?)

Answer 1

You need to make sure that you've altered your sys.path before you attempt to load any package that might depend on the altered path - otherwise your script will fail the moment it encounters and import statement. In other words, make sure your Main.py begins as:

import os
import sys

path = os.path.join(os.path.dirname(__file__), os.pardir)
sys.path.append(path)

from dirA.ClassA import ClassA

To ensure that the last import statement operates on the altered path.