A budget tracker

The problem

Build a program that keeps track of income and spending from typed commands, and gives a clear report by category.

Requirements

• Commands add income, add an expense with a category, and show a report
• Each transaction is stored as a dictionary or an object in a list
• A report shows the total for each category and the overall balance, in neat columns
• Bad commands and bad numbers give a clear message and do not stop the program
• The logic is in small functions, with no printing inside the calculation functions
• Tests with assert cover totals and edge cases such as an empty list

Technologies

• Python
• Dictionaries and lists
• Functions
• Exceptions
• f-strings

Step by step

1. Decide on the shape of one transaction, and write one by hand.
2. Write a function that adds a transaction to the list, and test it with assert.
3. Write functions that work out the balance and the total for each category.
4. Write the report function, using format codes to line up the columns.
5. Write the loop that reads a command and calls the right function.
6. Add try and except around converting numbers, with helpful messages.
7. Add a dictionary of commands in place of a chain of if statements.
8. Test unusual inputs: no transactions, unknown categories and negative amounts.

Expected result

A program you can run and type commands into, which never crashes on bad input and always shows correct totals.

How it is evaluated

• Totals are correct, including for an empty list
• Bad input is handled with a clear message
• Functions are small and do one job each
• The report lines up correctly
• Tests exist and pass

Ways to improve it

• Save the transactions to a file with the json module
• Add monthly budgets and warnings
• Show a simple text bar chart for each category