code: def find_by_external_tracker(self, url, id_):
          
          payload = {
              'include_fields': ['id', 'summary', 'status'],
              'f1': 'external_bugzilla.url',
              'o1': 'substring',
              'v1': url,
              'f2': 'ext_bz_bug_map.ext_bz_bug_id',
              'o2': 'equals',
              'v2': id_,
          }
          d = self.call('Bug.search', payload)
          d.addCallback(self._parse_bugs_callback)
          return d
docs: Find a list of bugs by searching an external tracker URL and ID.
  
          param url: ``str``, the external ticket URL, eg
                     "http://tracker.ceph.com". (Note this is the base URL.)
          param id_: ``str``, the external ticket ID, eg "18812".
          returns: deferred that when fired returns a list of ``AttrDict``s
                   representing these bugs.