Pywikibot is a Python-based framework to write bots for MediaWiki (more information).
Thanks to work in Google Code-in, Pywikibot now has a script called download_dump.py. It downloads a Wikimedia database dump from http://dumps.wikimedia.org/, and places the dump in a predictable directory for semi-automated use by other scripts and tests.
This script downloads big files, a progress bar or another indicator can be really useful.
You must avoid using external libraries for this. For reference, please read:
It would be even better if something like 105.2M/2.1G can be shown alongside the progress bar. (Not required)
You are expected to provide a patch in Wikimedia Gerrit. Documentation on Gerrit is available.