code: def max_shape_id(self):
          
          id_str_lst = self.xpath('//@id')
          used_ids = [int(id_str) for id_str in id_str_lst if id_str.isdigit()]
          return max(used_ids) if used_ids else 0
docs: Maximum int value assigned as @id in this slide.
  
          This is generally a shape-id, but ids can be assigned to other
          objects so we just check all @id values anywhere in the document
          (XML id-values have document scope).
  
          In practice, its minimum value is 1 because the spTree element itself
          is always assigned id="1".