'Returns a string representation of this model.'

def __unicode__(self):

    return u',    '.join([u'{}    user:    {}'.format(type(self).__name__, self.user_id), u'course    version:    {}'.format(self.course_version), u'grading    policy:    {}'.format(self.grading_policy_hash), u'percent    grade:    {}%'.format(self.percent_grade), u'letter    grade:    {}'.format(self.letter_grade), u'passed    timestamp:    {}'.format(self.passed_timestamp)])
