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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 uint8_3(self, val1, val2, val3):
 """append a frame containing 3 uint8"""

        try:
            self.msg += [pack("BBB", val1, val2, val3)]
        except struct.error:
            raise ValueError("Expected uint8")
        return self