docs: def get_cds_ranges_for_transcript(self, transcript_id):
          """ obtain the sequence for a transcript from ensembl
          """
          
          headers = {"content-type": "application/json"}
          
          self.attempt = 0
          ext = "/overlap/id/{}?feature=cds".format(transcript_id)
          r = self.ensembl_request(ext, headers)
          
          cds_ranges = []
          for cds_range in json.loads(r):
              if cds_range["Parent"] != transcript_id:
                  continue
              
              start = cds_range["start"]
              end = cds_range["end"]
              
              cds_ranges.append((start, end))
          
          return cds_ranges