I'm aware that I can manually code in a proxy with user/password, but is it possible to get Python to just pull the proxy settings AND authentication from IE?
For simple authentication (basic, digest), yes.  Simply make sure your system's proxy settings (e.g, in IE) are in the format:
joe:password@proxy.example.com:3128
If your proxy is using some other more complicated form of authentication (e.g., ntlm, kerberos), this is not so easy.
Can I get Python to use an authenticated Proxy without userinput?