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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sar(computation: BaseComputation) -> None: """ Arithmetic bitwise right shift """

    shift_length, value = computation.stack_pop(num_items=2, type_hint=constants.UINT256)
    value = unsigned_to_signed(value)

    if shift_length >= 256:
        result = 0 if value >= 0 else constants.UINT_255_NEGATIVE_ONE
    else:
        result = (value >> shift_length) & constants.UINT_256_MAX

    computation.stack_push(result)