One file is fine for a small program. Real projects grow, so we split the code into several files and folders. This is how a modern Python project looks:

learn-python/
├── pyproject.toml        ← name, Python version, packages (pytest lives here)
├── .python-version
├── main.py               ← the program starts here
├── pirates/              ← your own code, split into files (a "package")
│   ├── __init__.py       ← empty file that says: this folder is a package
│   └── treasure.py
└── tests/
    └── test_treasure.py  ← tests for the code in pirates/

• A folder with an __init__.py file is a package. Each .py file in it is a module.
• You use code from a module with from pirates.treasure import share_treasure.
• Tests live in tests/, and pytest finds every file that starts with test_.

Bigger projects and libraries put the packages in a src/ folder: src/learn_python/. That is what uv init does when you leave out --no-package. Same idea, one folder deeper.

You will see this at the bottom of almost every main.py:

def main() -> None:
    ...


if __name__ == "__main__":
    main()

• When you run a file (uv run main.py), Python sets __name__ to "__main__", so main() is called.
• When another file imports it, __name__ is the file's name instead, so nothing runs by accident.
• That is what makes it possible to test your functions without starting the whole program.

This example has two files. Click the tab pirates/treasure.py to read the locked file, then press Run. Try to:

• Share 500 coins between 9 pirates instead.
• Remove the last two lines. What happens when you run it? Why?

The locked file pirates/ship.py has a function crew_size. Import it, use it in main() to print The crew has 5 pirates, and make sure main() only runs when the file is started directly.

In your learn-python project, make the folder pirates with an empty __init__.py and this file:

def share_treasure(coins: int, pirates: int) -> tuple[int, int]:
    """Return how many coins each pirate gets, and how many are left over."""
    each = coins // pirates
    left_over = coins % pirates
    return each, left_over

Add a test for it:

from pirates.treasure import share_treasure


def test_share_treasure():
    assert share_treasure(100, 7) == (14, 2)
    assert share_treasure(10, 5) == (2, 0)

uv run pytest
ruff check .
ty check

All green? Commit it with git. You now have a real, tested Python project. 🏴‍☠️

You know variables, constants, types, operators, decisions, loops, functions and how a project is put together. That is the foundation of every program ever written.

Now you choose what to build, and in which language:

Talk to your instructor about your idea. 🏴‍☠️