Understanding the Purpose of if __name__ == '__main__' in Python

In Python, the if __name__ == '__main__': statement is a common pattern used to determine whether the current module is being executed as the main program.

Distinguishing script execution from import: When a file is run directly, the __name__ variable is set to __main__ ; when the same file is imported, __name__ holds the module's name.

Preventing code execution on import: By placing code inside the if __name__ == '__main__': block, you ensure that the code runs only when the file is executed as a script, not when it is imported by other modules.

Example module (my_module.py):

# my_module.py

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

def helper_function():
    print("This is a helper function.")

if __name__ == '__main__':
    main()

Running the module directly:

python my_module.py

Output:

This is the main function.

Importing the module from another script (another_script.py):

# another_script.py
import my_module
my_module.helper_function()

When another_script.py is executed, the output is:

This is a helper function.

Note that my_module.main() is not called because the if __name__ == '__main__': condition is false during import.

Typical uses:

Testing code – place test routines inside the block so they run only when the module is executed directly.

Main program logic – keep the entry point of an application inside the block.

Avoiding side effects – prevent actions such as opening database connections or configuring loggers from running on import.

Extended example with additional functions:

# my_module.py

def main():
    print("This is the main function.")
    print("Running as a script.")

def helper_function():
    print("This is a helper function.")

def test_helper_function():
    print("Testing helper function...")
    helper_function()

if __name__ == '__main__':
    # Code executed only when run directly
    main()
    test_helper_function()
else:
    # Code executed when imported
    print(f"Module {__name__} has been imported.")

Running python my_module.py produces:

This is the main function.
Running as a script.
Testing helper function...
This is a helper function.

Importing the module and calling my_module.helper_function() yields:

Module my_module has been imported.
This is a helper function.

Using this pattern lets a module act both as a reusable library and as an executable script, giving you fine‑grained control over when code runs.