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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 set_credentials(self, username, password=None, region=None, tenant_id=None, authenticate=False):
 """ Sets the username and password directly. Because Rackspace auth uses the api_key, make sure that any old values are cleared. """

        self.api_key = None
        super(RaxIdentity, self).set_credentials(username, password=password,
                region=region, tenant_id=tenant_id, authenticate=authenticate)