'Returns and caches (for future access) the results of
a bulk retrieval of all subsection grades in the course.'

def _get_bulk_cached_subsection_grades(self):

    if (self._cached_subsection_grades is None):
        self._cached_subsection_grades = {record.full_usage_key: record for record in PersistentSubsectionGrade.bulk_read_grades(self.student.id, self.course_data.course_key)}
    return self._cached_subsection_grades
