---

checkdigit is a pure Python library built for identification numbers. You want to validate a credit card number, or maybe even calculate a missing digit on an ISBN code? We've got you covered 😎.

Want to know more? Check out the API Reference and documentation!

Installation

MacPorts 🍎

sudo port install py-checkdigit

PyPi 🐍

pip install checkdigit

✨ Features

• PEP 561 compatible, with built in support for type checking.
• Capable of calculating missing digits or validating a block of data.
• Extensive in-code comments and docstrings to explain how it works behind the scenes. 🪄

✅ Supported Formats

• Even and odd binary parity
• Bookland
• CRC (credit to @sapieninja)
• EAN-13
• GS1 (credit to @OtherBarry)
• ISBN-10
• ISBN-13
• Luhn
• UPC-A

For each of these formats, we provide functions to validate them and calculate missing digits.

Do you have any formats that you'd like to see supported? 🤔 Feel free to raise an issue, or even to send a pull request!

🔨 Contributing

• Issue Tracker: https://github.com/harens/checkdigit/issues
• Source Code: https://github.com/harens/checkdigit

Any change, big or small, that you think can help improve this project is more than welcome 🎉.

As well as this, feel free to open an issue with any new suggestions or bug reports. Every contribution is appreciated.

🏗 Setup

First, fork the project to your account. Then, run the following with your GitHub handle in place of INSERT_GITHUB_NAME:

git clone https://github.com/INSERT_GITHUB_NAME/checkdigit
poetry install && poetry shell
pre-commit install

🏛 Project structure

checkdigit
├── scripts
│   ├── format.sh
│   └── tests.sh
├── checkdigit
│   ├── gs1.py
│   ├── isbn.py
│   ├── luhn.py
│   └── etc.
└── tests

Each new format goes into a separate file which is named accordingly. Similar formats (e.g. ISBN-10 and ISBN-13) should go in the same file.

Before submitting any new changes, please run the format.sh and tests.sh scripts beforehand. Thank you :)

📚 Building the Docs

The documentation can be found in docs/source.

We can use sphinx-autobuild to continuously rebuild the docs when changes are made.

sphinx-autobuild docs/source docs/_build/html

🎪 File structure

Each of the Python files follow the same general format:

# License + File docstring

from checkdigit._data import cleanse, convert


def calculate(data: str) -> str:
    """Determines check digit.

    Args:
        data: A string of data missing a check digit

    Returns:
        str: The single missing check digit (not the whole block of data)
    """
    # This helps to deal with user formatting inconsistencies
    # e.g. spaces, hyphens, etc.
    data = cleanse(data)

    # Deals with 10 or 11 being the possible check digit
    return convert(...)


def validate(data: str) -> bool:
    """Validates a block of data from the check digit.

    Args:
        data: A string representing a full block of data

    Returns:
        bool: A boolean representing whether the data is valid or not
    """
    data = cleanse(data)

    # Remove the check digit and see if it matches
    return calculate(data[:-1]) == data[-1]


def missing(data: str) -> str:
    """Returns the missing digit from a block of data.

    Args:
        data: A string with a question mark in the place of a missing digit.

    Returns:
        A string representing the missing digit (not the whole block of data)
    """
    data = cleanse(data)

    return ...

For similar data formats, the names can be adjusted accordingly (e.g. validate10 for ISBN-10 and validate13 for ISBN-13).

Contributors ✨

Thanks goes to these wonderful people (emoji key):

Timothy Langer ⚠️ 📖

Charlie Wilson 💻 ⚠️

Max Bowman 💻 ⚠️

This project follows the all-contributors specification. Contributions of any kind welcome!

📙 License

This project is licensed under GPL-3.0-or-later.