Pysync has both a demonstration implementation of the rsync and related algorithms in pure Python, and a high speed librsync Python extension. The pure Python is not fast and is not optimized, however it does work and provides a simple implementation of the algorithm for reference and experimentation. It includes a combination of ideas taken from librsync, xdelta, and rsync. The librsync Python extension is less flexible and harder to understand, but is very fast.
python-fchksum is a module used to find checksums of files (or stdin). It supports md5, crc32, cksum, bsd-style sum, and sysv-style sum. The advantage of using fchksum over the Python md5 and zlib(.crc32) modules is both ease of use and speed. You only need to tell it the filename, and the work is done by C code.
uTorrent.py is a Python module for accessing the interface exposed by the uTorrent Web UI. Current features include getting and setting uTorrent parameters, viewing information and statistics on torrents and files, and setting torrent state and file priorities. Small example utilities are included. Note that the download file is a 7zip archive, not a PNG image.