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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 encode(self):
 """Encode the DAT packet. This method populates self.buffer, and returns self for easy method chaining."""

        if len(self.data) == 0:
            log.debug("Encoding an empty DAT packet")
        data = self.data
        if not isinstance(self.data, bytes):
            data = self.data.encode('ascii')
        fmt = b"!HH%ds" % len(data)
        self.buffer = struct.pack(fmt,
                                  self.opcode,
                                  self.blocknumber,
                                  data)
        return self