Understanding Python's __name__ Variable: Purpose, Values, and Practical Examples

Python developers often encounter the built‑in __name__ variable, typically used in a conditional like if __name__ == '__main__': to control script execution. This article walks through the purpose of __name__ , the values it can take, and how to leverage it for modular code reuse.

What does __name__ do? It is a special attribute present in every Python module. Its value depends on how the module is executed: when the file is run as the main program, __name__ equals the string '__main__' ; when the file is imported, __name__ is set to the module’s filename (without the .py extension).

Possible values of __name__

• Direct execution: __name__ == '__main__' . • Imported as a module: __name__ == 'module_name' .

Case 1 – Running a script directly

Consider nameScript.py containing:

def myFunction():
    print('Variable __name__ is ' + __name__)

def main():
    myFunction()

if __name__ == '__main__':
    main()

When executed, Python first sets __name__ to '__main__' , defines the functions, evaluates the if statement as true, and calls main() , which in turn calls myFunction() and prints '__main__' .

Case 2 – Importing the script as a module

Another script importingScript.py imports nameScript.py :

import nameScript as ns
ns.myFunction()

During import, Python sets nameScript.py 's __name__ to 'nameScript' . The if __name__ == '__main__' block evaluates to false, so main() is not called. After import, importingScript.py can call ns.myFunction() , which prints the module’s __name__ value 'nameScript' .

Summary

The article demonstrated how the __name__ variable behaves differently when a Python file is executed directly versus when it is imported, allowing developers to write modules that can both provide reusable functionality and act as standalone scripts.