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