code: def cursor_position_col(self):
          
          # (Don't use self.text_before_cursor to calculate this. Creating
          # substrings and doing rsplit is too expensive for getting the cursor
          # position.)
          _, line_start_index = self._find_line_start_index(self.cursor_position)
          return self.cursor_position - line_start_index
docs: Current column. (0-based.)