code: def on_clear(self, event):
          
          dia = pmag_menu_dialogs.ClearWD(self.parent, self.parent.WD)
          clear = dia.do_clear()
          if clear:
              # clear directory, but use previously acquired data_model
              if self.data_model_num == 2.5:
                  self.parent.er_magic = builder.ErMagicBuilder(self.parent.WD, self.parent.er_magic.data_model)
              elif self.data_model_num == 3:
                  self.parent.contribution = cb.Contribution(self.parent.WD,
                                                             dmodel=self.parent.contribution.data_model)
docs: initialize window to allow user to empty the working directory