Python - ModuleNotFoundError: No module named

Question

I'm new in Python and I'm having the following error with this simple example:

This is my project structure:

python_project
.
├── lib
│   ├── __init__.py
│   └── my_custom_lib.py
└── src
    ├── __init__.py
    └── main.py

And this is the error when I execute the src/main.py file:

☁  python_project  python src/main.py

Traceback (most recent call last):
  File "src/main.py", line 3, in <module>
    from lib import my_custom_lib
ImportError: No module named lib

If I move the main.py file to the root and then I execute this file again, works... but is not working inside src/ directory

This is my main.py:

from lib import my_custom_lib

def do_something(message):
        my_custom_lib.show(message)

do_something('Hello World!')

Note: When I execute the same code from Pycharm is working fine, but not from my terminal.

Answer 1

Your PYTHONPATH is set to the current directory from the program you execute. So if you're executing something inside a directory src, it will never be able to find the directory lib because it's outside the path. There's a few choices;

• Just move lib/ into src/ if it belongs to your code. If it's an external package, it should be pip installed as Henrique Branco mentioned.
• Have a top-level script outside of src/ that imports and runs src.main. This will add the top-level directory to python path.
• In src/main.py modify sys.path to include the top-level directory. This is usually frowned upon.
• Invoke src/main.py as a module with python -m src.main which will add the top-level directory to the python path. Kind of annoying to type, plus you'll need to change all your imports.