def not_in(a, b, msg=None):
    'Assert a in not b, with repr messaging on failure.'
    assert (a not in b), (msg or ('%r is in %r' % (a, b)))
Assert a in not b, with repr messaging on failure.
def not_in(a, b, msg=None):
    
    assert (a not in b), (msg or ('%r is in %r' % (a, b)))