Why __name__ == '__main__'?

So, what does if __name__ == '__main__': mean?

Why it Matters?

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It is a way to ensure that a specific block of code runs only when the Python script is executed directly, and not when it’s imported as a module.

What is __name__?

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The __name__ is a built in variable in Python. It represents the current module’s name.

When we run a Python script, Python will assign __main__ to the __name__ variable if the script is the main program being executed.

Example

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Here, we have a Python script display_name.py with a define function called display to output the parameter name.

# display_name.py
def display(name):
  print(f'Hello, {name}')

if __name__ == '__main__':
  user_name = input('Enter name: ')
  display(user_name)

In this script (above), the following block will execute only if we run the script directly.

if __name__ == '__main__':
  user_name = input('Enter name: ')
  display(user_name)

This has been enforced by if __name__ == '__main__':.

What if we have another script, which we need to reuse the function display but we do not want to execute the block of code above?

Here is another Python script which like to reuse the display function.

# another_script.py
from display_name import display
name = 'Foo'
display(name)

It is all about making our code reusable. With if __name__ == '__main__':, it allows us to create Python script that can be imported as module, and reuse the function within.

When the first script display_name.py is imported as a module, the code inside the if __name__ == '__main__': will not be executed.

Summary

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With if __name__ == '__main__'::

• It is handy way to reuse function within a large Python project.
• It allows reuse of functions and classes from one script into another without running the whole script every time.
• It helps keeping things clean and organized.
• It helps creating versatile Python module.