if __name__ == "__main__" in Python

✅ Quick Example First

def add(a, b):
    return a + b

def test():
    print("Testing add:", add(2, 3))

if __name__ == "__main__":
    test()

What happens?

• Run this file → Output: Testing add: 5 ✅
• Import this file in another script → Output: (nothing) ❌ But you can still call add() from the other file.

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🤔 What Is __name__ == "__main__"?

This is a special line in Python that lets your file run code only when executed directly, not when imported by another file.

It’s not a function. It’s not magic. It’s just a check.

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🔄 The Core Idea

When you run a Python file, Python automatically sets a built-in variable called __name__.

Then it does this:

Situation	What __name__ becomes
You run the file directly	"__main__"
You import the file in another script	The file’s module name

✅ What does "__main__" mean?

It means “this is the starting point of the program”. When Python sets __name__ = "__main__", it’s marking this file as the one that was executed, not imported.

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🔍 Behind the Scenes

When Python starts running the file, it sets:

__name__ = "__main__"

But when the file is imported, it sets:

__name__ = "filename"

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🧱 Why Use This?

Use Case	Why It’s Useful
✅ Writing reusable modules	Code won’t auto-run when imported elsewhere
✅ Testing functions in the file	You can run it to test, but keep it clean when imported
✅ Keeping your code organized	Keeps script logic separate from definitions

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🧠 Summary Table

What You Do	What Python Sets __name__ To	What Runs?
Run file directly	"__main__"	Code under if __name__ runs ✅
Import file from another file	"module_name"	Code under if __name__ does NOT run ❌

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🪄 Final Advice for Beginners

• Always use if __name__ == "__main__" to keep your code clean and reusable.
• Think of it like a “main entry point” for your program.
• Great for testing parts of your code without triggering them on import.