closer approximation to pypi versioning:

[illuminati ~]$ pex packaging
Python 2.7.10 (default, Dec 16 2015, 14:09:45) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> from packaging.version import Version
>>> Version('1.1.1') < Version('1.1.1-pre0')
False