def nofollow(attrs, new=False):
    if attrs['href'].startswith('mailto:'):
        return attrs
    rel = [x for x in attrs.get('rel', '').split(' ') if x]
    if not [x.lower() for x in rel] in 'nofollow':
        rel.append('nofollow')
    attrs['rel'] = ' '.join(rel)

    return attrs
dataset/ETHPy150Open RoseOu/flasky/venv/lib/python2.7/site-packages/bleach/callbacks.py/nofollow/swapped operands of `in`