> Quoting Antoine Pitrou ...

> I suppose 172.18.2.7:3128 is the address:port of the your proxy, 
right?

Yes ...

> In which case, urllib seems to do the right thing. When talking to an
HTTP proxy, requests are of the form "GET http://site.com/path", rather
than "GET /path". It's up to the proxy to strip the host part of the URL
when forwarding the request to the target server.

This being said ... 

> (but I suppose tracd could also be more permissive and allow the "GET
http://site.com/path" variant. It seems Apache does)

... It works with Apache (I am talking about trac once again ...) 
therefore I will report this issue to Trac devs instead ...

Thnx a lot ! Sorry if I caused you any trouble ...