In httplib.py, line 336, the following code appears: 

    def _set_hostport(self, host, port):
        if port is None:
            i = string.find(host, ':')
            if i >= 0:
                port = int(host[i+1:])
                host = host[:i]
            else:
                port = self.default_port
        self.host = host
        self.port = port

Ths code breaks if the host string ends with ":", so that
int("") is called.  In the old (1.5.2) version of this 
module, the corresponding int () conversion used to be 
enclosed in a try/except pair: 

                try: port = string.atoi(port)
                except string.atoi_error:
                    raise socket.error, "nonnumeric port"

and this fixed the problem.  
Note BTW that now the error reported by int is 
"ValueError: invalid literal for int():"
rather than the above string.atoi_error. 

I found this problem while downloading web pages, 
but unfortunately I cannot pinpoint which page 
caused the problem. 

Luca de Alfaro