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