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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 get_extended_key(self):
 """Get the extended key. Extended keys contain the network bytes and the public or private key. """

        network_hex_chars = hexlify(
            chr_py2(self.network.SECRET_KEY))
        return ensure_bytes(network_hex_chars + self.get_key())