__main__.py

mypackage/
├── __init__.py
└── __main__.py

• This file is used to define the entry point of a Python package.
• When a directory is used as a package (contains an __init__.py file), and it is executed as the main program (using python -m <package>), the __main__.py file in that package is executed.

main.py

• This file is often used as the entry point for a standalone Python script or a simple program.
• The if __name__ == "__main__": block ensures that the main() function is only called if the script is executed directly and not imported as a module elsewhere.

# main.py
def main():
    print("This is the main function.")

if __name__ == "__main__":
    main()