I am implementing backup scripts in python. I\'m trying to keep things cross platform. I hear there is a python based rsync implementation: http://pypi.python.org/pypi/rsync.py<
Here is another rsync implementation in Python:
Alternative : pysync - implementation of the rsync and related algorithms in pure Python, and a high speed librsync Python extension
Another alternative: http://code.google.com/p/pyrsync/
I know that rdiff-backup is written in python and use an rsync-like algorithm. It use librsync. Note that rdiff-backup is not a replacement for rsync, so it will not fill your needs. But you can take a look at librsync and see how rdiff-backup use it.
Here is the algorythm (not sure if it helps you out):
http://code.activestate.com/recipes/577518-rsync-algorithm/