🧮 Python-Based Calculator Application

📌 Overview

This project is a fully modular and extensible calculator application built with Object-Oriented Programming (OOP) and design patterns to ensure maintainability, scalability, and testability.

The application follows core software engineering principles, including:

• SOLID Principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion)
• DRY (Don't Repeat Yourself)
• GRASP (General Responsibility Assignment Software Patterns)
• Separation of Concerns (Modular architecture)

It provides an interactive REPL (Read-Eval-Print Loop) where users can execute mathematical operations, manage calculation history, and extend functionality through a plugin system.

🛠 Features

✔️ Supports fundamental arithmetic operations (Add, Subtract, Multiply, Divide)
✔️ Implements a REPL-based command execution system
✔️ Saves and loads calculation history using Pandas & CSV
✔️ Implements plugin support for extending functionality dynamically
✔️ Includes comprehensive unit tests with pytest and code coverage analysis
✔️ Uses design patterns to enforce maintainability and extensibility

📽️ Demo Video

🎬 Click here to watch the demo

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📐 Architecture & Design Patterns Used

This project follows industry-standard design patterns to ensure modularity and reusability:

1️⃣ Facade Pattern

• Where? calculations.py (Manages Pandas operations)
• Why? Encapsulates the complexity of loading, saving, and managing history using Pandas, providing a simple interface for other components.

2️⃣ Command Pattern

• Where? commands/ (Handles REPL commands dynamically)
• Why? Enables commands like add, subtract, history to be executed independently while maintaining loose coupling.

3️⃣ Factory Method Pattern

• Where? calculations.py
• Why? Instantiates the history manager dynamically while allowing subclassing if needed.

4️⃣ Singleton Pattern

• Where? calculations_global.py
• Why? Ensures only one instance of the history manager exists throughout the application.

5️⃣ Strategy Pattern

• Where? operations.py
• Why? Dynamically selects the appropriate calculation strategy (e.g., addition, subtraction, multiplication, division).

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🛠 Installation & Setup

Prerequisites

Ensure you have Python 3.12 or higher installed.

Clone the Repository

git clone https://github.com/jesusgaud/Python-based_calculator_app.git
cd Python-based_calculator_app

Create a Virtual Environment

python -m venv venv
source venv/bin/activate  # Mac/Linux
venv\Scripts\activate      # Windows

Install Dependencies

pip install -r requirements.txt

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🚀 Usage

To start the REPL interface, run:

python main.py

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Available Commands

Command	Description
add x y	Adds two numbers
subtract x y	Subtracts y from x
multiply x y	Multiplies two numbers
divide x y	Divides x by y
history	Displays past calculations
exit	Exits the program

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🧪 Running Tests & Code Quality Checks

Run Unit Tests

pytest

Run Tests with Coverage

pytest --cov

Run Linting Checks (Pylint)

pytest --pylint

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🛠 Plugin System

The calculator application supports plugin-based extensibility, allowing new operations to be added dynamically.

Adding a New Plugin

1. Navigate to app/plugins/
2. Create a new Python file (e.g., modulus.py)
3. Implement a new operation as a function
4. The system will automatically detect and register the plugin

Example Plugin (modulus.py)

Create a new plugin file inside app/plugins/ and define an operation:

def operation(a, b):
    return a % b

To enable plugin discovery, ensure the following is included:

from app.operations import load_plugins
load_plugins()

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🛠 Development & Contribution Guidelines

Branching Strategy

• main → Stable production branch
• feature-branches → Feature development
• bugfix-branches → Fixes for existing issues

How to Contribute

1. Fork the repository on GitHub.
2. Create a new branch for your feature or fix:

   git checkout -b feature-new-command

3. Make your changes and commit:

   git commit -m "Added new command feature"

4. Push to GitHub:

   git push origin feature-new-command

5. Open a Pull Request (PR) to GitHub for review.

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📜 License

This project is licensed under the MIT License.

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📞 Contact

For questions, please reach out via GitHub Issues.