This is, to my knowledge, the official (and only) way to structure a Python project. There are two to create an executable file to start everything.

Option 1: Native Script

Many Python projects offer a Bash script (on UNIX-like systems) or a Windows .bat file that will run the python3 -m cards98 command. I see this a lot.

Option 2: Python Script

This is the method I'd recommend, as it's the most portable.

Outside of your top-level package, you can write a separate Python script, such as run.py or cards98.py, and then use that to execute your main function.

For example, in cards98/__main__.py, you can put this...

def main():
    # The logic for starting your application.

if __name__ == "__main__":
    main()

And then, outside of the cards98 package, create the file cards98.py, with the following:

#!/usr/bin/env python3
from cards98.__main__ import main
main()

To start your Python application, just double-click cards98.py.

P.S. Thanks for bringing up this situation. I realized I never addressed it in the book!