@protected
    def doc_field_length(self, docnum, fieldid):
        fieldid = self.schema.to_number(fieldid)
        if fieldid not in self._scorable_fields:
            raise FieldConfigurationError("Field %r does not store lengths" % fieldid)
        
        pos = self._fieldnum_to_scorable_pos[fieldid]
        return self.doclengths.at(docnum, pos)
dataset/ETHPy150Open dokipen/whoosh/src/whoosh/filedb/filereading.py/SegmentReader.doc_field_length/original