Changing DNS settings using PyObjC
Looks like there are issues with PyObjC that cause this to not work, however you may be able to find a way around it by using a different solution. If I were you, and my situation allowed it, I would just call the system command line tools to set the DNS servers.
According to OSXDaily, you can do this with:
networksetup -setdnsservers (Network Service) (DNS IP)If you have cross platform requirements this is obviously less than desirable.