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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 countries(self):
 """ Access the countries :returns: twilio.rest.voice.v1.dialing_permissions.country.CountryList :rtype: twilio.rest.voice.v1.dialing_permissions.country.CountryList """

        if self._countries is None:
            self._countries = CountryList(self._version, )
        return self._countries