If we're talking about implementations in various languages, I might as well link to my capped backoff with jitter implementation for python.

https://github.com/ekimekim/pylibs/blob/master/libs/backoff....

(apologies for the long link, I keep all my one-file python libs in a single git repo for sanity. I think i've uploaded this one to pypi, where it's available under the name "backoff")