__name__ == "__main__" in Python

What It Is In Python, every file (module) has a built-in variable called __name__.
Its value depends on how the file is being used:
• ✅ When run directly:
The value of __name__ is set to "__main__".
• 📦 When imported as a module:
The value of __name__ is set to the module’s name (i.e., the filename without .py).

A module is basically a Python file (.py) containing variables, functions, or classes.

The statement:

Python

if __name__ == "__main__":

is used to determine whether a Python script is being executed directly or imported into another script.

Code inside this block executes only when the file runs directly, not when it’s imported as a module.

Why It’s Useful:

1. Encourages Code Reuse
   You can define functions, classes, or constants in a file and use them both for:
   • Direct testing or execution.
   • Importing into other programs as reusable modules.
2. Prevents Unwanted Execution During Import
   Any test or print statements inside the if __name__ == "__main__": block won’t run when the file is imported.
3. Promotes Modularity and Clean Design
   Helps keep your codebase organized and ensures that modules have a single, clear entry point.

Example: Simple demonstration.

Python

# file: mymodule.py

# Define a function
def greet(name):
    print(f"Hello, {name}!")

if __name__ == "__main__":
    # This code runs only when the file is executed directly
    greet("Ashish")

• When run directly: python mymodule.py • Output: Hello, Ashish!

• Imported in another file:

Python

# file: test.py
import mymodule

mymodule.greet("World") 

Output: Hello, World!

Note: The code inside if __name__ == "__main__": in mymodule.py does not execute when imported.

Explanation: