Many of us have seen the:

import something

def function():
    pass

if __name__ == '__main__':
    # function calls here...
    pass

in one documentation or the other, but what is it?

• __main__
• '__name__'

Short Answer

It protects users from accidentally invoking the script when they didn't intend to. It also helps the user identify whether the file has to be executed or not. The lack of it will make identification harder for the user.

Long Answer

In a large process, there are 2 types of files:

1. Files that contain function definitions.
2. Files that call those functions and display output.

Files of type 1 do not need to be executed since they won't display output and simply define the functions and classes and constants used.

On the other hand, files of type 2 need to be executed since they display and output. To help the user identify that this file has to be execute, one uses if __name__ == '__main__'

When the interpreter runs a module (that is the main program), the __name__ variable will have the value __main__.

print(f"__name__ = {__name__}")    # __name__ = '__main__'

But If the code is importing from another module, then the __name__ variable will be set to that module’s name.

import something

print(f"__name__ = {__name__}")    # __name__ = 'something'

Conclusion

We can use an if __name__ == "__main__" block to allow or prevent parts of code from being run when the modules are imported.