code: def uclust_fasta_sort_from_filepath(
          fasta_filepath,
          output_filepath=None,
          tmp_dir=gettempdir(),
          HALT_EXEC=False):
      
      if not output_filepath:
          _, output_filepath = mkstemp(dir=tmp_dir, prefix='uclust_fasta_sort',
                                       suffix='.fasta')
  
      app = Uclust(params={'--tmpdir': tmp_dir},
                   TmpDir=tmp_dir, HALT_EXEC=HALT_EXEC)
  
      app_result = app(data={'--mergesort': fasta_filepath,
                             '--output': output_filepath})
  
      return app_result
docs: Generates sorted fasta file via uclust --mergesort.