Recently, my team members starting seeing intermittent install errors from pip. Python packages that had installed days, hours, or even minutes ago suddenly became unavailable when pip install was run.

To make matters worse, the problem was not reproducable. Sometimes, everything in our requirements.txt would install just fine. Other times, Python packages as basic as setuptools and httplib2 would fail to install. The error message from pip read:

"No distributions at all found for..."

and

"Could not find any downloads that satisfy the requirement..."

We tried bypassing our proxy, switching from WiFi to wired ethernet, destroying and rebuilding our Vagrant box, and even switching to a different internet connection. After days of debugging, I discovered that our pip, installed by apt-get, was woefully out of date. I upgraded from pip 1.1 to pip 8.0 using

pip install --upgrade pip

Et voilà. The problem was fixed. Our packages went back to being installed seamlessly.

N.B., you may see SNIMissingWarning and InsecurePlatformWarning messages in the console output after upgrading. You should be able to ignore them with no functional impact.