Fix - NameError: name '__main__' is not defined in Python

Fix - NameError: name __main__ is not defined in Python #

The Python "NameError: name __main__ is not defined" occurs when we forget to wrap the special name __main__ in quotes. To solve the error, wrap the name __main__ in quotes, e.g. "__main__".

Here is an example of how the error occurs.

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# ⛔️ NameError: name '__main__' is not defined. Did you mean: '__name__'?
if __name__ == __main__:
    print('Module is ran directly')

To solve the error we have to wrap the special name __main__ in quotes.

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# ✅ using the string __main__
if __name__ == '__main__': # 👈️ wrap in quotes
    print('Module is ran directly')

When a Python module is imported, the __name__ is set to the module's name.

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import math

print(math.__name__)  # 👉️ "math"

Usually this is the name of the Python file without the .py extension.

However, if the module is ran directly, its __name__ is set to the string "__main__".

Top-level means that this module imports all other files that the program needs.

You can use the __name__ variable to check if the module is running in the top-level environment.

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if __name__ == '__main__':
    print('Module is ran directly')

We compare the __name__ variable to the string "__main__" and if the condition is met, we know that the module is ran directly and is not initialized from an import statement.