Unfortunately these may change between networks.  EX: At one office, the proxy url can be 192.168.1.2, and at another it could be 10.0.1.100.

http://docs.python-requests.org/en/latest/user/advanced/#proxies

details a sweet part of requests that can use environment variables.  So, I can type into bash HTTP_PROXY="192.168.1.2", and the python library should take care of it!  Maybe instead it would be a viable option to "suggest" to users to set an environment variable for the host through -h 

OR  add a --proxy line that will "take in" PROXY['http'] so it can be still used in this fashion.

Nice work though!  It was a good idea.  It's awesome to make sure this works in a myriad of environments, such as corporate ones where the Internet isn't as easy to access :P

:+1: