How to use 'python list difference between elements' in Python

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def set_difference_update(arr, *others):
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    pass

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def sorted_list_difference(expected, actual):
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    i = j = 0
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    missing = []
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    unexpected = []
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    while True:
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        try:
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            e = expected[i]
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            a = actual[j]
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            if e < a:
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                missing.append(e)
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                i += 1
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                while expected[i] == e:
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                    i += 1
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            elif e > a:
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                unexpected.append(a)
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                j += 1
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                while actual[j] == a:
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                    j += 1
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            else:
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                i += 1
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                try:
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                    while expected[i] == e:
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                        i += 1
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                finally:
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                    j += 1
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                    while actual[j] == a:
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                        j += 1
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        except IndexError:
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            missing.extend(expected[i:])
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            unexpected.extend(actual[j:])
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            break
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    return (missing, unexpected)