Open-source GIS implementation of the Huff model

As scw says in his comment the code itself seems to make use of some basic processing and loops so could probably be rewritten quite quickly in Python and Shapely.

However if you are looking for a script take a look at the following written in R..and German: http://www.reymann.eu/wp-content/uploads/2010/06/GravitationsgesetzHuff.R

Google Translate seems to indicate it provides the "Calculation of the purchase probability Huff's law of gravitation"

Linked to from http://www.reymann.eu/wettbewerbsanalysen/einzugsgebiet

It does have a copyright notice on it so maybe contact the author for further details. If you take out all the lines that print to the screen it seems R can implement it very concisely.