It appears to me as if the behavior of parse_version('dev') has changed with setuptools-0.6c9, but this change is not documented on the setuptools documentation. Assuming pv=parse_version, the documentation implies that pv('a') < pv('b') < pv('c') == pv('rc') < pv('d') == pv('dev'). but it turns out that pv('dev') == pv('@') < pv('a'). I suggest the documentation say something like the following: A pre-release tag is a series of letters that are alphabetically before "final". Some examples of prerelease tags would include alpha, beta, a, c, dev, and so on. You do not have to place a dot before the prerelease tag if it's immediately after a number, but it's okay to do so if you prefer. Thus, 2.4c1 and 2.4.c1 both represent release candidate 1 of version 2.4, and are treated as identical by setuptools. In addition, there are three special prerelease tags that are treated as if they were the letter c: pre, preview, and rc. So, version 2.4rc1, 2.4pre1 and 2.4preview1 are all the exact same version as 2.4c1, and are treated as identical by setuptools. Furthermore, dev is a special tag that is always less than any other character tag. It is treated as the equivalent of the character '@'. Any objections?