💰 Python CLI Expense Tracker

A menu-driven, console-based expense tracker built entirely with Core Python. Users can log expenses, review their spending history, and see a running total — all backed by a simple, dependency-free accumulator pattern.

🎓 Built as Project 2 of the Python Programming Internship at DecodeLabs, focused on data accumulation, state management, and defensive input handling in backend logic.

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📖 Description

The Expense Tracker simulates the core of a real financial ledger: numbers come in one at a time, get validated, and get added to a running total that persists for the life of the session. It's a small program, but it's built around the same fundamental pattern (total += new_value) that powers much larger financial and analytics systems.

The entire application lives in a single, well-documented Python file and uses nothing beyond the standard language — no databases, no file storage, no third-party packages.

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🏢 Internship Context

Program	Python Programming Internship
Organization	DecodeLabs
Project	Project 2 — Expense Tracker
Focus Area	Data accumulation & stateful console logic
Constraint	Core Python only (no external libraries, no persistence)

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✨ Features

• Add Expense — enter an amount and add it to the running total using the accumulator pattern (total += new_expense).
• View Expense History — see every expense recorded during the current session, numbered in the order it was entered.
• View Total Expenses — see the total number of expenses logged and the running total spent.
• Delete Last Expense — remove the most recently added expense and automatically subtract it back out of the total.
• Reset Expense Tracker — clear all recorded expenses and reset the total to zero, with a yes/no confirmation step to prevent accidental data loss.
• Exit — a sentinel-controlled, clean shutdown of the program.

Built-in input safety (every feature is protected by this):

• Rejects non-numeric input instead of crashing.
• Rejects negative expense amounts.
• Rejects empty input and zero-value amounts.
• Rejects out-of-range or non-numeric menu selections.
• Gracefully handles Ctrl+C / Ctrl+D (KeyboardInterrupt / EOFError) instead of throwing a raw traceback.

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🛠️ Tech Stack

• Language: Python 3.x
• Libraries: None — Core Python only (input(), print(), lists, loops, conditionals, functions)
• Storage: In-memory only (a Python list), scoped to the current session
• Interface: Command-line / console

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📁 Folder Structure

Expense_Tracker_Project/
├── main.py                  # Complete application source code
├── README.md                 # Project documentation (this file)
├── LICENSE                   # MIT License
├── .gitignore                 # Python-specific ignore rules
├── PROJECT_STRUCTURE.md       # Detailed explanation of every file
└── screenshots/                # Real terminal screenshots of the app
    ├── home.png
    ├── add-expense.png
    ├── expense-history.png
    ├── total-expenses.png
    ├── delete-expense.png
    ├── reset-tracker.png
    ├── invalid-input.png
    ├── negative-expense.png
    └── exit.png

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⚙️ Installation

Clone the repository:

git clone https://github.com/PawanChoudhary0607/Python-Expense-Tracker.git
cd Python-Expense-Tracker

No dependencies to install — the project runs on the Python standard library alone.

Requirements: Python 3.x

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▶️ How to Run

python3 main.py

On Windows:

python main.py

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🔄 Program Flow

Start
  │
  ▼
Display Menu (1-6)
  │
  ▼
Read & Validate Menu Choice
  │
  ├── 1 → Add Expense        → Validate amount → total += amount
  ├── 2 → View History        → Print all recorded expenses
  ├── 3 → View Total          → Print count + running total
  ├── 4 → Delete Last Expense → Remove last item → total -= amount
  ├── 5 → Reset Tracker       → Confirm → Clear list → total = 0
  └── 6 → Exit                → Print goodbye message → break loop
  │
  ▼
Loop back to Menu (while True)

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💻 Example Output

Welcome to the DecodeLabs Expense Tracker!

==============================
      EXPENSE TRACKER
==============================
1. Add Expense
2. View Expense History
3. View Total Expenses
4. Delete Last Expense
5. Reset Expense Tracker
6. Exit
==============================

Enter your choice (1-6): 1
Enter expense amount: 250

Expense of 250.00 added successfully.
Running Total: 250.00

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📸 Screenshots

Home Menu

Add Expense

View Expense History

View Total Expenses

Delete Last Expense

Reset Expense Tracker

Invalid Menu Input Handling

Negative / Invalid Expense Handling

Exit

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🎯 Learning Outcomes

Building this project reinforced several core backend-engineering concepts:

• The accumulator pattern — how total = total + new_value forms the backbone of any system that processes a continuous stream of numeric data (ledgers, counters, running statistics).
• State vs. amnesia in loops — the importance of initializing state outside a loop so it persists across iterations, rather than resetting it on every pass.
• Defensive coding — treating all user input as untrusted by default, validating type, sign, and emptiness before it ever reaches business logic.
• Sentinel-controlled program flow — using a dedicated exit value to cleanly break out of an otherwise infinite while True loop.
• Separating logic from display — keeping calculation (the "model") distinct from what gets printed to the user (the "view"), even in a single-file script.

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🚀 Future Improvements

• Add expense categories (e.g., Food, Travel, Utilities).
• Persist expenses between sessions (file or database storage).
• Add date/timestamp tracking for each expense.
• Add a monthly or weekly spending summary.
• Add CSV export for use in spreadsheets.

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👤 Author

Pawan Choudhary B.Tech CSE (AI & ML) Python Programming Intern @ DecodeLabs

GitHub: github.com/PawanChoudhary0607

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📄 License

This project is licensed under the MIT License.