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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 revocable(self):
 """ ``False`` if this signature is marked as being not revocable. Otherwise, ``True``. """

        if 'Revocable' in self._signature.subpackets:
            return bool(next(iter(self._signature.subpackets['Revocable'])))
        return True