code: def item_coords(self, table_item):
          
          for row_key in self.children.keys():
              for item_key in self.children[row_key].children.keys():
                  if self.children[row_key].children[item_key] == table_item:
                      return (int(row_key), int(item_key))
          return None
docs: Returns table_item's (row, column) cordinates.
          Returns None in case of item not found.
  
          Args:
              table_item (TableItem): an item instance