code: def store(self):
          '''
          Record the current value of each variable X named in track_vars in an
          attribute named X_hist.
  
          Parameters
          ----------
          none
  
          Returns
          -------
          none
          '''
          for var_name in self.track_vars:
              value_now = getattr(self,var_name)
              getattr(self,var_name + '_hist').append(value_nowf store(self):
          '''
          Record the current value of each variable X named in track_vars in an
          attribute named X_hist.
  
          Parameters
          ----------
          none
  
          Returns
          -------
          none
          '''
          for var_name in self.track_vars:
              value_now = getattr(self,var_name)
              getattr(self,var_name + '_hist').append(value_now)
docs: Record the current value of each variable X named in track_vars in an
          attribute named X_hist.
  
          Parameters
          ----------
          none
  
          Returns
          -------
          none