What If I Could Make My Own Module?

The problem...

You have functions that work. Functions you've tested, functions you trust.

And you keep copying them from one script to another.

There's a better way.

The idea!

Any Python file can be a module.

You already import from Python's standard library — import random, import math. Those are just Python files sitting somewhere on your machine.

Your files work the same way. Write a function in one file. Import it in another. Use it anywhere.

Making it real

Create a file called utils.py:

# utils.py

def greet(name):
    return f"Hello, {name}."

def celsius_to_fahrenheit(c):
    return c * 9/5 + 32

Now in another file — same folder:

# main.py
import utils

print(utils.greet("Raven"))
print(utils.celsius_to_fahrenheit(100))

Output:

Hello, Raven.
212.0

That's it. utils.py is your module. main.py imports it.

from import — bring in one function

from utils import greet

print(greet("Wolf"))

No prefix needed. Just the function name.

Why this matters

One function. Ten scripts that need it. You write it once — in one place. You fix it once. You test it once.

That's not just convenience. That's how real projects are structured. Logic lives in modules. Scripts import what they need. Nothing is duplicated.

The rule

The module file must be in the same folder as the script that imports it — or Python won't find it.

project/
    utils.py      ← your module
    main.py       ← imports from utils

if __name__ == "__main__"

When Python imports a file, it runs it. If your module has code outside functions — it runs on import too. That's usually not what you want.

The fix:

# utils.py

def greet(name):
    return f"Hello, {name}."

if __name__ == "__main__":
    print(greet("Raven"))   # only runs when utils.py is run directly
                            # not when it's imported

This block runs only when the file is executed directly — not when imported. Use it for tests, demos, or any code you don't want running on import.

Heads up!

• The module file must be in the same folder as the importing script
• Don't name your module the same as a standard library module — random.py would shadow Python's own random
• Code outside functions runs on import — use if __name__ == "__main__" to protect it
• Any .py file is a potential module — no special setup needed

The mindset shift

Stop thinking: "I'll write everything in one file."

Start thinking: "What belongs together? What will I reuse? That goes in its own module."

What you should understand now

• Any .py file can be imported as a module
• import utils — access with utils.function()
• from utils import function — use directly
• Module must be in the same folder as the importing script
• if __name__ == "__main__" protects code from running on import