Writing Your Own Module in Python

A module in Python is simply a .py file that contains Python code — variables, functions, classes, or any executable statements.

By writing your own modules, you can:

Organize your code Avoid repetition Improve readability Reuse code across multiple programs or projects

Why Write Your Own Modules?

How to Create a Module

1️⃣ Create a .py file — this is your module. 2️⃣ Define variables, functions, or classes inside the file. 3️⃣ Import the module into other Python files.

Example 1: Create a Simple Module

File: mymath.py

# This is my custom module
 
def add(a, b):
    return a + b
 
def subtract(a, b):
    return a - b

Example 2: Import and Use Your Module

File: main.py

import mymath
 
print("Sum:", mymath.add(10, 5))
print("Difference:", mymath.subtract(10, 5))

Sum: 15
Difference: 5

Example 3: Using from module import

from mymath import add
 
print("Sum:", add(20, 10))

Sum: 30

Where to Place Your Module

Example 4: Organizing with Packages

If you want to organize multiple modules:

myproject/
│
├── mypackage/
│   ├── __init__.py
│   ├── module1.py
│   ├── module2.py
│
└── main.py

In main.py:

from mypackage import module1
 
module1.some_function()

Example 5: Checking __name__

def greet():
    print("Hello from my module!")
 
if __name__ == "__main__":
    greet()

Hello from my module!

Explanation:

• The __name__ variable allows a module to detect if it’s run as a script or imported as a module.

Summary

• A module is simply a .py file.
• Helps you split code into reusable parts.
• Import your module using import module_name.
• Use __init__.py to create packages of modules.
• Organizing code into modules improves readability, testing, and maintainability.

In the next section, we will explore Installing Packages — how to bring in external modules from the wider Python ecosystem.

Would you like me to proceed with the next topic — Installing Packages — in the same style? Just confirm! 🚀