Unclear what's happening with Dunder Main

Hi there Joshua Richardson 👋

I'll try my best to break things down.

1. What is __name__?

• In every Python file, there is a built-in variable called __name__.
• When you run a file directly (like python my_script.py), __name__ becomes "__main__".
• But if you import that file from another Python file, __name__ becomes the name of the module (i.e., the filename without .py).

1. What does if __name__ == "__main__" mean?

It means:

"Only run this block of code beneath if this file is being run directly, not if it's being imported somewhere else."

This lets you write a file that can be:

• Run as a standalone script or
• Imported as a module without running everything automatically

1. Why is this important?

Let’s say you have a file called math_tools.py:

# math_tools.py
def add(a, b):
    return a + b

print("Doing some math...")  # <- This line always runs

if __name__ == "__main__":
    print(add(2, 3))  # <- This only runs when math_tools.py is run directly

If you run: python math_tools.py

You'll see:

Doing some math...
5

But if you import it from another file:

# another_script.py
import math_tools

and run this file, you'll only see:

Doing some math...

You won’t see the print(add(2, 3)) part—because the file wasn’t the "main" one being run. This allows for code to only be run in certain situations, great for testing things like that.

__name__ A built-in variable that tells you how a file is being run.

"__main__" The value of __name__ when the file is run directly.

if __name__ == "__main__" Run this code only when the file is run directly.

Where to put it? Usually in script files, but can be in modules for testing/debugging.

I hope this helps a bit.