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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 post_build(self, pkt, pay):
 """ add padding to the frame if required. note that padding is only added if pay is None/empty. this allows us to add # noqa: E501 any payload after the MACControl* PDU if needed (piggybacking). """


        if not pay:
            under_layers_size = self._get_underlayers_size()

            frame_size = (len(pkt) + under_layers_size)

            if frame_size < 64:
                return pkt + b'\x00' * (64 - frame_size)

        return pkt + pay