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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 update(self, quality_score, issue=values.unset):
 """ Update the FeedbackInstance :param unicode quality_score: The call quality expressed as an integer from 1 to 5 :param FeedbackInstance.Issues issue: Issues experienced during the call :returns: Updated FeedbackInstance :rtype: twilio.rest.api.v2010.account.call.feedback.FeedbackInstance """

        return self._proxy.update(quality_score, issue=issue, )