10. Modules & Packages

The Import System

When you import a file, Python runs the entire file from top to bottom.

__name__ == "__main__"

This pattern prevents code from running when a file is imported.

python
def run():
    print("Running app...")

if __name__ == "__main__":
    # This block only runs if you do: python file.py
    # It does NOT run if you do: import file
    run()

Packages

A folder becomes a package if it has an __init__.py file (though optional in recent Python, it's still good practice).