code: def supported_peptide_lengths(self):
          
          if 'supported_peptide_lengths' not in self._cache:
              length_ranges = set(
                  network.supported_peptide_lengths
                  for network in self.neural_networks)
              result = (
                  max(lower for (lower, upper) in length_ranges),
                  min(upper for (lower, upper) in length_ranges))
              self._cache["supported_peptide_lengths"] = result
          return self._cache["supported_peptide_lengths"]
docs: (minimum, maximum) lengths of peptides supported by *all models*,
          inclusive.
  
          Returns
          -------
          (int, int) tuple