Why do we use if __name__ == '__main__' in Python

13 feb 2024 2 min di lettura
Why do we use if __name__ == '__main__' in Python
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Python, known for its simplicity and readability, hides a small snippet of code that, despite its frequent appearance in scripts around the world, often leaves newcomers perplexed: if __name__ == '__main__':. This line, far from being a simple standard, is a powerful construct that provides control over the execution of your code. Let's demystify this secret and discover the power and purpose behind it.

Understanding __name__

To grasp the importance of if __name__ == '__main__':, we must first understand what __name__ means in Python. Every module in Python has a built-in attribute called __name__. The value of __name__ is set to '__main__' when the module runs as the main program. Otherwise, the value of __name__ is set to the module name. This distinction is crucial to understanding the functionality enabled by this conditional statement.

The purpose of if __name__ == '__main__'

The main use of if __name__ == '__main__': is to control the execution of code. When writing a Python script, you may want certain code to run when the script is executed directly, but not when imported as a module into another script. This is where if __name__ == '__main__': comes into play. It allows you to distinguish between the two scenarios, enabling a dual use case for your Python files: as reusable modules or as standalone scripts.

Use cases and benefits

  • Reusable code: By encapsulating code that should only run when the script is executed directly inside this conditional, you make your script reusable as a module. Other scripts can import functions, classes, or variables without executing script-level code.
  • Testing and Debugging – This template is incredibly useful for testing. You can include test code in the script that runs the tests when the script is run directly. This means you can test functions in the same file, keeping the tests close to your code.
  • Script entry points: For larger applications or packages, if __name__ == '__main__': serves as a clear entry point. It is immediately clear to other developers where to find the main logic of the script or which part of the code triggers execution.

Practical example

Let's understand the difference with a practical example:

Create Script: Consider a simple Python script named script.py:

def greet(name):
 print(f"Hello, {name}!")


 if __name__ == "__main__":
 print("The script is run directly")

Run script: When we run script.py directly using python script.py, the output will be:

Hello, Alice!
 The script is run directly

The if __name__ == "__main__": block is executed because __name__ is set to "__main__" when the script is run directly.

Import script into another: Now let's enter import script.py into another Python script named main.py:

import script

Run new script: When we run main.py using python main.py, the output will be:

Hello, Alice!

This time, the if __name__ == "__main__": block in script.py is not executed. The reason is __name__ which is set to "script", the name of the script when imported, not "__main__".


The if __name__ == '__main__': construct is a testament to Python's flexibility, allowing scripts to be both reusable modules and stand-alone programs. By understanding and using this pattern, developers can write more modular, testable, and maintainable code. This little line of code reveals a significant aspect of Python programming, demonstrating that even the most seemingly cryptic features have profound purposes. Embrace it, and you'll find your Python code not only more powerful, but also more versatile.

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