Vigenère Cipher 🔐

A minimal, well-tested implementation of the classic Vigenère cipher with an installable command-line interface (CLI) and a small importable Python module.

• Purpose: educational utility and lightweight library for encoding/decoding text with a repeating-key Vigenère cipher. Preserves letter case and leaves non-letter characters unchanged.
• License: MIT

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Features

• Clean, documented implementation in vigenere_cipher.py.
• CLI: vigenere (installed as an entry point) supporting --encode/--decode.
• Keyword validation: only ASCII alphabetic keywords are accepted.
• Unit tests with pytest and type checks with mypy.
• GitHub Actions workflow for CI (black, mypy, pytest).

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Installation

Clone the repository and install in editable (development) mode:

git clone <repo-url>
cd vigenere-cipher
pip install -e .

You can also install the development tools:

pip install -r requirements-dev.txt

Supported Python versions: 3.8+

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Usage

CLI

Encode a message:

vigenere --encode --keyword KEY --message "Hello, World!"

Decode a message:

vigenere --decode --keyword KEY --message "ciphertext"

Read from stdin (useful in scripts or pipelines):

echo "text" | vigenere --encode --keyword key

If the vigenere console script is not on your PATH (Windows/Powershell limitations), run the module directly:

python -m vigenere_cipher --help

Importing the library

Use the module directly from Python code:

from vigenere_cipher import vigenere_encode, vigenere_decode

cipher = vigenere_encode("Hello, World!", "key")
plain = vigenere_decode(cipher, "key")

Behavior notes:

• keyword must be a non-empty string of ASCII letters (A–Z, a–z).
• Case of alphabetic characters is preserved; punctuation and numbers are left unchanged.

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Tests & Quality

Run the test suite using pytest:

python -m pytest -q

Code formatting and style:

• Black is used for formatting (configuration in pyproject.toml).
• mypy is configured for lightweight static typing checks.

CI is configured in .github/workflows/ci.yml to run black, mypy and pytest on push/PR.

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Contributing

Contributions are welcome — please open issues or PRs. Suggested ways to help:

• Add more tests, edge cases, or property-based tests (Hypothesis).
• Improve CLI features (file input/output, encoding options).
• Add packaging metadata and release automation.

Please follow the existing style (Black + type hints) and add tests for new behaviors.

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License

This project is licensed under the MIT License. See LICENSE for details.

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