Get to know the brief and start building your calculators from scratch while recapping important object-oriented and software engineering principles such as the Don't Repeat Yourself (DRY) principle. 

Introducing the challenge

BasicCalculator

FinancialCalculator

Software engineering principles

Principles of Software Engineering

Relative imports

Absolute imports

Inheritance reuses code

Multilevel inheritance

Create the mortgage calculator class

Introduction to the Case Study

The basics are done, and now it's time to spruce them up! Continue with adding documentation and automated testing, and extend the functionality even further.

Documenting your new class

Using docstring

Using dir()

Overview of Automated Testing

Using doctest

Features of doctest

Custom Class

Using dir on a class

Add a method to an inherited class

Write a Python Module

The main code is written so now it's time to make sure everything works as it should and follows the best practices. Learn how to review, refactor, and improve your code, as well as run more comprehensive tests. 

Maintainability

Using good variable names

"""Module for mortgage functionality"""
def calculateMonthlyInterestRate(annual_interest_rate):
    """This function calculates monthly interest given anual rate given the annual interest rate.
    """
    if annual_interest_rate >= 0:
        return annual_interest_rate / 12
    return 0.00

MONTHLY_RATE = calculateMonthlyInterestRate(.06)
print(MONTHLY_RATE)


"""Module for mortgage functionality"""
def calculate_monthly_interest_rate(annual_interest_rate):
    """This function calculates monthly interest given anual rate given the annual interest rate.
    """
    if annual_interest_rate >= 0:
       return annual_interest_rate / 12
    return 0.00

MONTHLY_RATE = calculate_monthly_interest_rate(.06)
print(MONTHLY_RATE)


Pylint

Reviewing and refactoring code

Code Review

Refactor Code

Testing

Benefits of Unit Testing

Test the code using pytest

Congratulations!


Learn to build a real-world application—a mortgage calculator—while mastering core software engineering principles. You’ll design modular Python code, use inheritance to expand functionality, and ensure quality through best practices like the DRY principle, PEP 8 compliance, and automated testing with pytest. By the end, you’ll have the skills to create efficient, maintainable, and scalable software solutions for real-world challenges.

This course offers a hands-on introduction to software engineering by guiding you through the development of a practical application: a mortgage calculator. You’ll learn how to calculate monthly payments based on key inputs like loan amount, interest rate, and loan term. Along the way, you’ll apply essential software engineering principles to create code that is efficient, modular, and maintainable.<br><br>
<h2>What You’ll Build</h2>
Using Python, you’ll design and implement a mortgage calculator that evolves from a basic tool into a robust solution. Starting with simple modules, you’ll expand the functionality using inheritance to create advanced calculators, including one that handles financial computations. This hands-on project will help you understand real-world software development techniques and how to structure scalable code.<br><br>
<h2>Techniques You’ll Use</h2>
Throughout the course, you’ll follow best practices like the DRY (Don’t Repeat Yourself) principle and modularity to organize your code effectively. You’ll adhere to PEP 8 standards, use tools like Pylint to maintain code quality and write automated tests with pytest to ensure your application’s reliability. By the end of the course, you’ll have the skills to design, implement, and test real-world software solutions with confidence.

Intermediate Object-Oriented Programming in Python

Software Engineering Principles in Python

Build real-world applications with Python—practice using OOP and software engineering principles to write clean and maintainable code.

Building Software in Python

Case Study: Building Software in Python

Building Applications with OOP in Python

Code Review

Case Study: Building Software in Python

Hands-on interactive exercise