As you may have noticed, development of pyCardDAV has been dormant for some time and I herewith declare it officially dead. While I always wanted to rewrite it on top of vdir, I lack the time to do it (and all hacking time I found was spent on khal). A good alternative seems to be khard.
As I still use pyCardDAV myself, I will still fix bugs against Davical for the foreseeable future, but don't expect anything else.