code: def get_proxy(self, proxy_address):
          
          if not proxy_address:
              return None
          hostport = extract_proxy_hostport(proxy_address)
          return self.proxies_by_hostport.get(hostport, None)
docs: Return complete proxy name associated with a hostport of a given
          ``proxy_address``. If ``proxy_address`` is unkonwn or empty,
          return None.