Did you try it again, in case there a was temporary network issue?
Not only that, but other users have reported exactly the same problem, as I pointed out. See https://community.letsencrypt.org/t/certbot-auto-fails-on-debian-wheezy-hangs-on-installing-python-packages/61061/4 This is no "temporary network issue" affecting one user.
Do you have any trouble downloading large files from pypi outside Python? e.g.
No, none whatsoever. After I installed curl, the line you suggested executed successfully, downloading the 12MB file in a couple of seconds.