__main__ — Top-level script environment — Python 3.9.0 documentation

# `__main__` — Top-level script environment

`'__main__'` is the name of the scope in which top-level code executes. A module’s __name__ is set equal to `'__main__'` when read from standard input, a script, or from an interactive prompt.

A module can discover whether or not it is running in the main scope by checking its own `__name__`, which allows a common idiom for conditionally executing code in a module when it is run as a script or with `python -m` but not when it is imported:

    if __name__ == "__main__":
        # execute only if run as a script
        main()

For a package, the same effect can be achieved by including a `__main__.py` module, the contents of which will be executed when the module is run with `-m`.