Packages and the Main Guard

Scenario: Importing a useful function unexpectedly runs the module's command-line program.

New words, in plain English

• Package - a directory grouping related Python modules
• __name__ - a special name identifying how a module was loaded
• Main guard - an if statement that runs CLI code only for direct execution

A package commonly includes __init__.py. Relative imports connect sibling modules. When a file is run directly, __name__ is "__main__"; when imported, it is the module name.

Analogy: A Python program is like a clear set of instructions for a careful helper: names label things, indentation groups steps, and errors explain where the helper became confused.

A small, real example

def main():
    print("running CLI")

if __name__ == "__main__":
    main()

Tip: Keep import-time behavior small and predictable.

Goal: Practice this idea in the py-modules-import challenge at /labs/python. Fix the broken program, run it yourself, then use check to prove the real end state.