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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_by_external_tracker(self, url, id_):
 """ 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. """

        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