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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 new_keys(self):
 """ Access the new_keys :returns: twilio.rest.api.v2010.account.new_key.NewKeyList :rtype: twilio.rest.api.v2010.account.new_key.NewKeyList """

        if self._new_keys is None:
            self._new_keys = NewKeyList(self._version, account_sid=self._solution['sid'], )
        return self._new_keys