<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def preferred_width(self, cli, max_available_width):
 """ Return the preferred width for this control. That is the width of the longest line. """

        text = token_list_to_text(self._get_tokens_cached(cli))
        line_lengths = [get_cwidth(l) for l in text.split('\n')]
        return max(line_lengths)