PIP_DOWNLOAD_CACHE

Specify a PIPDOWNLOADCACHE environment variable and pip will cache packages it downloads, then use the cached version in future instead of download it a second time. Really handy if, like me, you're a virtualenv junky and having large packages like Django installed in multiple virtual envs.

For example, add this to your .zshrc / .bashrc:

export PIP_DOWNLOAD_CACHE=$HOME/.pip-download-cache