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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 invalidate(self):
 """ Invalidates all non-identifier Properties this object has locally, causing the next access to re-fetch them from the server """

        for key in [k for k in type(self).properties.keys()
                if not type(self).properties[k].identifier]:
            self._set(key, None)

        self._set('_populated', False)