Unlock Python’s __name__: When to Use It and Why It Matters

You've probably seen the __name__ variable in many Python scripts; it often appears like this:

if __name__ == __main__:
    main()

In this article we dive into the built‑in __name__ variable, demonstrate how to use it in your Python modules, and explain what values it can take. __name__ is a special built‑in variable present in every Python module. Its value depends on how the code is executed: if the file is run directly, __name__ equals __main__; if the file is imported, __name__ equals the module's name.

Case 1 – Running the script directly

Assume we have nameScript.py with the following code:

def myFunction():
    print("变量 __name__ 的值是 " + __name__)

def main():
    myFunction()

if __name__ == __main__:
    main()

When you execute nameScript.py directly, Python first sets __name__ to __main__. The if condition evaluates to true, so main() runs and prints __main__.

Case 2 – Importing from another script

Now suppose we want to reuse myFunction() in another script called importingScript.py:

import nameScript as ns
ns.myFunction()

When importingScript.py runs, the imported module nameScript has its __name__ set to nameScript, so the if condition inside nameScript.py is false and main() is not called. After the import, you can call ns.myFunction(), which prints the module's name ( nameScript).

In summary, the __name__ variable lets you distinguish whether a module is being run as a script or being imported, enabling you to write code that can act both as a reusable module and as a standalone program.