def header_section(self):
        """Returns an ARFF header as a string."""
        # Header comment.
        s = ('% Weka ARFF file\n' +
             '% Generated automatically by NLTK\n' +
             '%% %s\n\n' % time.ctime())

        # Relation name
        s += '@RELATION rel\n\n'

        # Input attribute specifications
        for fname, ftype in self._features:
            s += (fname, ftype) % '@ATTRIBUTE %-30r %s\n'

        # Label attribute specification
        s += '@ATTRIBUTE %-30r {%s}\n' % ('-label-', ','.join(self._labels))

        return s
dataset/ETHPy150Open nltk/nltk/nltk/classify/weka.py/ARFF_Formatter.header_section/swapped operands of `%`