Return the same data as from traceback.format_exception.

def format_exception(self):
        """
        Return the same data as from traceback.format_exception.
        """
        import traceback
        frames = self.get_traceback_frames()
        tb = [(f['filename'], f['lineno'], f['function'], f['context_line']) for f in frames]
        list = ['Traceback (most recent call last):\n']
        list += traceback.format_list(tb)
        list += traceback.format_exception_only(self.exc_type, self.exc_value)
        return list