Script Entry Points

A reusable module should define functions without starting a complete workflow when another file imports it. A script, however, needs a clear place to begin. Python's conventional entry-point pattern supports both uses.

This is a reference page. Chapter 8 does not require the pattern, but you will see it in Python projects and documentation.

Put the workflow in main

Python sets the special name __name__ differently in two situations:

• When this file is run as a script, __name__ is "__main__", so main() runs.
• When another file imports it as a module, __name__ is the module's name, so the guarded call does not run.

The guard does not make a function reusable. Separating the calculation from file paths and printing does that. The guard only controls whether the script starts its workflow.

Running a module

Python can also run a module by its import name:

python -m report_app

In that case Python finds report_app as a module and runs it with __name__ set to "__main__". Use this form when a project's instructions define a runnable module. Do not add it merely to make a small one-file exercise look larger.