code: def clear(self):
          
          self.exposures = []
          self.exposure_labels = []
          self.exposure_combo_boxes = []
          self.exposure_edit_buttons = []
          self.mode = CHOOSE_MODE
  
          self.layer_purpose = None
          self.layer_mode = None
          self.special_case_index = None
  
          self.value_maps = {}
          self.thresholds = {}
  
          # Temporary attributes
          self.threshold_classes = OrderedDict()
          self.active_exposure = None
  
          self.list_unique_values = None
          self.tree_mapping_widget = None
  
          clear_layout(self.left_layout)
          clear_layout(self.right_layout)
docs: Clear current state.