docs: def extract_library_properties_from_selected_row(self):
          """ Extracts properties library_os_path, library_path, library_name and tree_item_key from tree store row """
          (model, row) = self.view.get_selection().get_selected()
          tree_item_key = model[row][self.ID_STORAGE_ID]
          library_item = model[row][self.ITEM_STORAGE_ID]
          library_path = model[row][self.LIB_PATH_STORAGE_ID]
          if isinstance(library_item, dict):  # sub-tree
              os_path = model[row][self.OS_PATH_STORAGE_ID]
              return os_path, None, None, tree_item_key  # relevant elements of sub-tree
          assert isinstance(library_item, string_types)
          library_os_path = library_item
  
          library_name = library_os_path.split(os.path.sep)[-1]
  
          return library_os_path, library_path, library_name, tree_item_key