code: def _transcript_feature_position_ranges(self, feature, required=True):
          
          if feature not in self._TRANSCRIPT_FEATURES:
              raise ValueError("Invalid transcript feature: %s" % feature)
  
          results = self.db.query(
              select_column_names=["start", "end"],
              filter_column="transcript_id",
              filter_value=self.id,
              feature=feature)
  
          if required and len(results) == 0:
              raise ValueError(
                  "Transcript %s does not contain feature %s" % (
                      self.id, feature))
          return results
docs: Find start/end chromosomal position range of features
          (such as start codon) for this transcript.