If you’re a researcher who’s ever written a Python script—maybe to analyze data, run simulations, or automate something—you’ve probably come across this line:

if __name__ == '__main__':

It looks mysterious. Almost magical. But what does it actually do?

In this post, we’ll break it down in simple terms, explain why it matters (especially for scientists and engineers), and show you how to use it properly in your own research scripts. You’ll also find a short video at the end if you prefer to watch rather than read.

What Is __name__ == '__main__'?

When Python runs a script, it creates a special built-in variable called __name__.

If you're running a script directly, like this:

python my_script.py

…then Python sets __name__ to the string '__main__'.

But if you're importing that script into another Python file, like this:

import my_script

…then __name__ is set to 'my_script'.

That’s where the conditional comes in:

if __name__ == '__main__':
    # do something

This tells Python:

"Only run this block of code if this file is being executed directly—not when it's imported."

Why It Matters for Researchers

Let’s say you’ve written a Python script to simulate disease spread:

def simulate_epidemic():
    # some brilliant epidemiology model
    print("Simulating outbreak...")

simulate_epidemic()

It works great! But what happens when you later want to reuse simulate_epidemic() in another file?

If you import the script like this:

from my_model import simulate_epidemic

Boom—it still runs simulate_epidemic()! Even though you didn’t ask it to. 😅

The Fix:

def simulate_epidemic():
    print("Simulating outbreak...")

if __name__ == '__main__':
    simulate_epidemic()

Now, the simulation only runs when the file is executed directly, not when it’s imported elsewhere.

This is super useful if you’re:

• Writing utility scripts for data cleaning or visualization
• Building pipelines that combine multiple scripts
• Sharing modules with your lab or collaborators

TL;DR

• __name__ is a special Python variable.
• It equals '__main__' when the file is run directly.
• Using if __name__ == '__main__': lets you separate executable code from importable functions.

It’s essential for writing modular, reusable, and clean Python code—especially in research.

Prefer to Watch?

Check out our short and fun explainer video here:
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Final Thought

That weird-looking line isn't so weird after all—it's just Python being polite. Now you can write scripts that behave exactly the way you want, no surprises.

Happy coding! 🚀