code: def fa2s2b(fastas):
      
      s2b = {}
      for fa in fastas:
          for seq in parse_fasta(fa):
              s = seq[0].split('>', 1)[1].split()[0]
              s2b[s] = fa.rsplit('/', 1)[-1].rsplit('.', 1)[0]
      return s2b
docs: convert fastas to s2b dictionary