A base-agnostic implementation of the Luhn Algorithm for Python. Useful for generating and verifying check digits.

# Baluhn: Base-agnostic Luhn

Baluhn provides a base-independent implementation of the Luhn algorithm for Python. It is useful for generating and verifying check digits in arbitrary bases.

From Wikipedia:

The Luhn algorithm or Luhn formula, also known as the "modulus 10" or "mod 10" algorithm, is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers in US and Canadian Social Insurance Numbers.

## Installation

Use pip install baluhn or python setup.py install.

## Usage

The baluhn module provides two functions: verify and generate.

generate calculates the Luhn check character for the given input string in the given base. This character should be appended to the input string to produce a valid Luhn string. verify tests whether or not a string is a valid Luhn string in the given base. By default, Baluhn operates in base 10:

>>> from baluhn import generate, verify
>>> verify('5105105105105100') # MasterCard test number
True
>>> value = '510510510510510' # note the missing check digit
>>> generate(value)
'0'
>>> verify(value + '0')
True
>>> verify(value + '7')
False

When operating in a base other than decimal, encoder and decoder callables should be supplied. The encoder should take a single argument, an integer, and return the character corresponding to that integer in the operating base. Conversely, the decoder should take a string containing a single character and return its integer value in the operating base. Note that the mapping between values and characters defined by the encoder and decoder should be one-to-one.

For example, when working in hexadecimal:

>>> hex_alphabet = '0123456789abcdef'
>>> hex_encoder = lambda i: hex_alphabet[i]
>>> hex_decoder = lambda s: hex_alphabet.index(s)
>>> value = 'a8b56f'
>>> generate(value, base=16, encoder=hex_encoder, decoder=hex_decoder)
'b'
>>> verify('a8b56fb', base=16, decoder=hex_decoder)
True
>>> verify('a8b56fc', base=16, decoder=hex_decoder)
False

## Author

Baluhn is written by Ben Hodgson and maintained by Four Digits.

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.

In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.