code: def make_gtf_filename(ensembl_release, species):
      
      ensembl_release, species, reference_name = normalize_release_properties(
          ensembl_release, species)
      return GTF_FILENAME_TEMPLATE % {
          "Species": species.capitalize(),
          "reference": reference_name,
          "release": ensembl_release,
      }
docs: Return GTF filename expect on Ensembl FTP server for a specific
      species/release combination