ok, I saw you added `highest_version` as an import (which uses `compare_version`) in `show.py`, but you're not using it.
so no need to refactor `pip search` as part of this, then?   
but if we do,  I think it should use pkg_resources.  the example in the commit you mention works fine in pkg_resources.:

```
>>> import pkg_resources
>>> l1 = pkg_resources.parse_version('1.1')
>>> l2 = pkg_resources.parse_version('1.1.2')
>>> l3 = pkg_resources.parse_version('1.1a1')
>>> l3 < l1 < l2
True
```