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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 dependent_phone_numbers(self):
 """ Access the dependent_phone_numbers :returns: twilio.rest.api.v2010.account.address.dependent_phone_number.DependentPhoneNumberList :rtype: twilio.rest.api.v2010.account.address.dependent_phone_number.DependentPhoneNumberList """

        if self._dependent_phone_numbers is None:
            self._dependent_phone_numbers = DependentPhoneNumberList(
                self._version,
                account_sid=self._solution['account_sid'],
                address_sid=self._solution['sid'],
            )
        return self._dependent_phone_numbers