@gen.coroutine
    def has_doc(self, doc_id):
        url = '{0}/{1}'.format(self.db_name, url_escape(doc_id))
        r = yield self._http_head(url)
        raise gen.Return(r['code'] == 200)
Return last item with a key <= k.  Raise ValueError if not found.
dataset/ETHPy150Open nephics/tornado-couchdb/couch/couch.py/AsyncCouch.has_doc--crossover with--dataset/ETHPy150Open tabatkins/bikeshed/bikeshed/SortedList.py/SortedList.find_le