code: def _filter_exact(self, term, field_name, field_type, is_not):
          
          if field_type == 'text' and field_name not in (DJANGO_CT,):
              term = '^ %s $' % term
              query = self._phrase_query(term.split(), field_name, field_type)
          else:
              query = self._term_query(term, field_name, field_type, stemmed=False)
  
          if is_not:
              return xapian.Query(xapian.Query.OP_AND_NOT, self._all_query(), query)
          else:
              return query
docs: Returns a query that matches exactly the un-stemmed term
          with positional order.
  
          Assumes term is not a list.