txretry provides a Twisted class, RetryingCall, that calls a function until it succeeds. A back-off iterator (a generator function that yields intervals) can be specified to customize the interval between retried calls. When/if the back-off iterator raises StopIteration the attempt to call the function is aborted. An instance of the RetryingCall class provides a start method that returns a Deferred that will fire with the function result or errback with the first failure encountered.

Usage of the class is described in the following blog post: http://blogs.fluidinfo.com/terry/2009/11/12/twisted-code-for-retrying-function-calls/