On Jul 10, 2014, at 1:47 PM, Christopher Armstrong <radix@twistedmatrix.com> wrote:

For what it’s worth, if you add an “a%n” to the end of a version, pip won’t install it unless you specify the version exactly. e.g., “tubes” version “0.1a1” won’t be found if you type “pip install tubes”, only “pip install tubes==0.1a1”.

Also "pip install --pre tubes", I believe.  Nevertheless, people put that into a config file somewhere and forget about it forever ;).