To reproduce:
- Launch a HTTP server listening on an Inet6 socket on, say, port 5555
- Try to connect using the IPv6 loopback: 
http = httplib.HTTPConnection('[::1]:5555')
http.request('GET', '/foo')
r = http.getresponse()
print r.status
- You get 400 (bad-request) instead of 404

It seems that's because the HTTP request is wrong. Python sends this header:
Host: ::1:5555
but it should be:
Host: [::1]:5555

I'm using python 2.5.2-1ubuntu1 on Intrepid.

Actually, this bug is present when you try to connect to any URL
containing an IP6 and a port.

So, we have the same problem when using, for example:
http = httplib.HTTPConnection('[2a01:8790:16d:0:218:de87:164:8745]:5555')

but
http = httplib.HTTPConnection('[2001:4860:0:1001::68]:80')

does work. Probably because we use the default HTTP port.

As per the RFC 2732 host header should be wrapped with []. I am
attaching patch for this too which is applied on trunk(2.7)

RFC 2732 Section three have the following details.

      host          = hostname | IPv4address | IPv6reference
      ipv6reference = "[" IPv6address "]"

The patch contains check for : and adding the brackets

Thanks for the patch. It would be better if you also added a test to
Lib/test/test_httplib.py (unless for some reason it's technically
impossible to do so).

Attaching the test patch