code: def dump(self, obj, key=None):
          
          if key is None:
              key = '_pickle'
          with preserve_current_directory():
              self.__file.cd()
              if sys.version_info[0] < 3:
                  pickle.Pickler.dump(self, obj)
              else:
                  super(Pickler, self).dump(obj)
              s = ROOT.TObjString(self.__io.getvalue())
              self.__io.reopen()
              s.Write(key)
              self.__file.GetFile().Flush()
              self.__pmap.clear()
docs: Write a pickled representation of obj to the open TFile.