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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 get_grades(self, login=None, promotion=None, **kwargs):
 """Get a user's grades on a single promotion based on his login. Either use the `login` param, or the client's login if unset. :return: JSON """


        _login = kwargs.get(
            'login',
            login or self._login
        )
        _promotion_id = kwargs.get('promotion', promotion)
        _grades_url = GRADES_URL.format(login=_login, promo_id=_promotion_id)
        return self._request_api(url=_grades_url).json()