code: def insert_completion(self, p_insert):
          
          start, end = self._surrounding_text
          final_text = start + p_insert + end
          self.set_edit_text(final_text)
          self.set_edit_pos(len(start) + len(p_insert))
docs: Inserts currently chosen completion (p_insert parameter) into proper
          place in edit_text and adjusts cursor position accordingly.