A while ago, Tim Peters mentioned in a check-in message:

"Change the version string from "2.2+" to "2.3a0".  distutils 
peels off
the first 3 characters of this string in several places, so for as 
long
as they remain "2.2" it confuses the heck out of attempts to 
build 2.3 stuff using distutils."

It's true; distutils does sys.version[:3] in a few places.
The attached patch factors this out so it'll be easier to 
change.  

(There's also a Python development issue here, namely when
the version number gets bumped in the CVS tree.)