Expense Report Refactoring Python Kata

Overview

This kata complements Clean Code: SOLID, Ep. 10 - Open-Closed Principle.

In this exercise, you'll practice refactoring code to adhere to the Open-Closed Principle (OCP). You'll be working with an expense report system that tracks different types of expenses and prints a final report.

Instructions

Exercise 1

The ExpenseReport class in the expense_report.py file generates an expense report. It iterates over a list of expenses, printing out a line for each expense and totaling up the amounts.

The current implementation, however, is complex and hard to understand, and it's not easy to modify or extend its behavior. It's your task to refactor this code to make it cleaner and more maintainable, while ensuring that it still correctly calculates and prints the report.

Make sure the program still behaves the same way after your refactoring. There's a unit test suite in place that checks that on a very rudimentary level by just looking at the output of the program.

Exercise 2

When you're done with refactoring, test the quality of your refactoring by implementing two additional scenarios:

1. Extend our system to handle two more types of expenses.

   1. Transportation. Surcharge: 5% of the expense amount.
   2. Supplies. Surcharge: No surcharge.

2. Add dynamic surcharge based on day of week.

   • For dinners on weekends, the surcharge is 15% of the expense amount.
   • For breakfasts on weekends, the surcharge is 10% of the expense amount.
   • On weekdays, the surcharges remain the same as before (10% for dinner and 5% for breakfast).

   You may need to add a date field to the Expense class to support this requirement. The date should be the date when the expense occurred.

   Note

   You can use the datetime module in Python to work with dates, and you can determine if a date is a weekend by using the following function:

   from datetime import datetime
   
   
   def is_weekend(date_str):
       date = datetime.strptime(date_str, "%Y-%m-%d")
       day_of_week = date.weekday()
       # If day of week is 5 or 6 (Saturday or Sunday), it's a weekend
       return day_of_week >= 5
   
   date_str = "2023-06-17"  # this is a Saturday
   print(is_weekend(date_str))  # this should print: True

Usage

You can import this project into Replit, and it will handle all dependencies automatically.

Prerequisites

• Python 3.8+
• pytest

Run main

make run

Run tests

make test