Learning Python in the Age of AI/

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Build the Functionality

Build the Functionality

Create the core features of the “Budget Tracker” project in this lesson.

We'll cover the following...

In the previous lesson, you:

  • Chatted with a simulated client and gathered needs.

  • Converted notes into functional requirements.

  • Created a clean skeleton of eight function stubs.

Now we’ll bring it to life. Starting with two core functions, then using AI to scaffold the rest. You’ll also get quick tests and a full reference solution.

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We’ll keep a tiny in-memory data model:

# globals (top of your file)
income = 0.0
# A list of expense dictionaries, e.g. [{"category": str, "amount": float}, ...]
expenses = []   # each entry: {"category": str, "amount": float}

Conventions we’ll use:

  • Positive amounts only.

  • Built-ins only, Python, no external libs / file I/O / classes.

Build the basics

We’ll implement add_income and add_expense first. These are the heartbeat of the app; everything else plugs into them.

add_income(amount)

Before we start coding our first function, let’s ...