<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _marker_line(self):
 # type: () -> str """Generate a correctly sized marker line. e.g. :return: str """

        output = ''
        for col in sorted(self.col_widths):
            line = self.COLUMN_MARK + (self.DASH * (self.col_widths[col] + self.PADDING * 2))
            output += line
        output += self.COLUMN_MARK + '\n'

        return output