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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 last_month(self):
 """ Access the last_month :returns: twilio.rest.api.v2010.account.usage.record.last_month.LastMonthList :rtype: twilio.rest.api.v2010.account.usage.record.last_month.LastMonthList """

        if self._last_month is None:
            self._last_month = LastMonthList(self._version, account_sid=self._solution['account_sid'], )
        return self._last_month