Python Cheat Sheet Part 03 - Functions & Modules

Suptojit Modak

March 18, 2026 March 18, 2026

Welcome to Cyber Supto! I'm Supto. In this Python Cheat Sheet series, we are learning Python in a quick, practical way with simple examples you can use while coding.

In Part 01 we covered Python basics and syntax, and in Part 02 we explored control flow like conditions and loops. In this part, we will focus on functions and modules, which help organize code and make programs reusable.

What is a Function?

A function is a reusable block of code that performs a specific task. Instead of writing the same code multiple times, you can define a function and call it whenever needed.

def greet():
    print("Hello from Cyber Supto")

greet()

The def keyword is used to define a function.

Function Parameters

Functions can accept inputs called parameters.

def greet(name):
    print("Hello", name)

greet("Supto")

This allows the function to work with different values.

Multiple Parameters

def add(a, b):
    print(a + b)

add(5, 3)

Functions can accept multiple parameters separated by commas.

Return Statement

The return keyword sends a result back from a function.

def multiply(a, b):
    return a * b

result = multiply(4, 5)
print(result)

Returning values makes functions more useful in larger programs.

Default Parameters

You can assign default values to parameters.

def greet(name="Guest"):
    print("Hello", name)

greet()
greet("Supto")

If no argument is provided, the default value is used.

Keyword Arguments

Python allows passing arguments by name.

def user_info(name, age):
    print(name, age)

user_info(age=20, name="Supto")

This improves readability and flexibility.

Arbitrary Arguments (*args)

Use *args when you don't know how many arguments will be passed.

def total(*numbers):
    print(sum(numbers))

total(1,2,3,4)

Arbitrary Keyword Arguments (**kwargs)

Use **kwargs for variable keyword arguments.

def profile(**data):
    print(data)

profile(name="Supto", role="Developer")

Lambda Functions

A lambda is a small anonymous function.

square = lambda x: x * x
print(square(5))

Lambda functions are useful for short operations.

What is a Module?

A module is a file that contains Python code such as functions, variables, or classes. Modules help organize large programs.

Importing a Module

import math

print(math.sqrt(16))

This imports the built-in math module.

Import Specific Functions

from math import sqrt

print(sqrt(25))

This imports only the required function.

Module Alias

You can rename modules using as.

import math as m

print(m.pi)

This makes code shorter and cleaner.

Creating Your Own Module

Create a file called utils.py:

def greet(name):
    print("Hello", name)

Then import it in another file:

import utils

utils.greet("Supto")

This helps organize large projects.

Useful Built-in Modules

math – mathematical operations
random – random number generation
datetime – date and time handling
os – operating system operations
sys – system-specific parameters

Quick Tips

Use functions to avoid repeating code
Keep functions small and focused
Use modules to organize large programs
Name functions clearly based on their task
Reuse functions whenever possible

Other Parts of This Python Cheat Sheet

This Python Cheat Sheet series on Cyber Supto is designed as a quick reference for developers and beginners learning Python.

Thanks for reading,
Cyber Supto.

Python