“main” in Python: What It Means and Why You Should Care

When you're new to Python, you might often see this line:

if __name__ == "__main__":

At first, it might seem cryptic, but once you understand it, you'll realize it's one of Python’s most useful features for writing clean, modular, and reusable code.

The __name__ Variable

Every Python file has a built-in variable called __name__.

• When a Python script is run directly, __name__ is set to "__main__".

• When a Python file is imported as a module, __name__ is set to the module’s name.

 Let's understand it with an example

FileName: HelloWorld.py

def greet():
    print("Hello from HelloWorld.py!")

if __name__ == "__main__":
    greet()

Case 1. Run directly

python HelloWorld.py

Output

Hello from HelloWorld.py!

Case 2. Import as a module

FileName: test.py

import HelloWorld
print("This is test.py")

If you import the above code in a module like

import HelloWorld
print("This is test.py")

It will generate output like 

This is test.py.

Here greet() is not called because the if __name__ == "__main__": block is skipped when the file is imported.

Why Use It?

Using if __name__ == "__main__": allows you to:

• Write code that can be used as a script and also imported as a module without side effects.
• Keep your code modular and reusable.
• Prevent certain code from running when the file is imported elsewhere.