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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 factors(self):
 """ Access the factors :returns: twilio.rest.authy.v1.service.entity.factor.FactorList :rtype: twilio.rest.authy.v1.service.entity.factor.FactorList """

        if self._factors is None:
            self._factors = FactorList(
                self._version,
                service_sid=self._solution['service_sid'],
                identity=self._solution['identity'],
            )
        return self._factors