docs: def save(self, *args):
          """ Save cache to file using pickle.
  
          Parameters
          ----------
          *args:
              All but the last argument are inputs to the cached function. The
              last is the actual value of the function.
          """
          with open(self.file_root + '.pkl', "wb") as f:
              pickle.dump(args, f, protocol=pickle.HIGHEST_PROTOCOL)