docs: def get_transcript_lengths(ensembl, transcript_ids):
      """ finds the protein length for ensembl transcript IDs for a gene
      
      Args:
          ensembl: EnsemblRequest object to request sequences and data
              from the ensembl REST API
          transcript_ids: list of transcript IDs for a single gene
      
      Returns:
          dictionary of lengths (in amino acids), indexed by transcript IDs
      """
      
      transcripts = {}
      for transcript_id in transcript_ids:
          # get the transcript's protein sequence via the ensembl REST API
          try:
              seq = ensembl.get_protein_seq_for_transcript(transcript_id)
          except ValueError:
              continue
          
          transcripts[transcript_id] = len(seq)
      
      return transcripts