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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 cipherprefs(self):
 """ A ``list`` of preferred symmetric algorithms specified in this signature, if any. Otherwise, an empty ``list``. """

        if 'PreferredSymmetricAlgorithms' in self._signature.subpackets:
            return next(iter(self._signature.subpackets['h_PreferredSymmetricAlgorithms'])).flags
        return []