How do I use functions from a different subdirectory in python with a virtual environment?

Question

I have a simple test project with the following file structure:

- Modules
    - .venv
    - code
        - main.py
    - package
        - __init__.py
        - mod.py

mod.py

def add(arg1, arg2):
    print(arg1 + arg2)

main.py

from package.mod import add
add(1,2)

__init__.py is empty.

I want to run add() from main.py but when I try it doesn't let me import it saying: ModuleNotFoundError: No module named 'package'

Now, I've seen some other posts about modifying the PATH variable at run-time which I tried and it didn't work. I suspect it's because none of these solutions used a virtual-environment.