GTINs (Global Trade Item Number) are ubiquitous. We commonly see them as barcodes on products. They come in several different types and names such as EAN, UPC or ISBN etc.
Recently, I needed to validate a set of GTINs stored in a file. To my surprise (unless my Google-fu is getting weak), I could not find any libraries written in Python for doing this. The algorithm (http://www.gs1.org/barcodes/support/check_digit_calculator) is simple enough to knock together in a few minutes, but I think the requirement is common enough to warrant a ready-made library.
My first attempt at this can be found at https://github.com/charithe/gtin-validator. This module can validate GTIN-8, GTIN-12, GTIN-13 and GTIN-14 codes in either numeric or string forms. Dashes in the code (as is common with ISBN numbers) are supported.
I have never worked on a publicly available Python module before. Neither am I a professional Python developer. The chances are that there are certain parts in the code that do not conform to conventions. However, it's fully open source - so anybody can contribute to make it better.