'Updates the grade for the course. Also updates subsection grades
if self.force_update_subsections is true, via the lazy call
to self.grader_result.'

def update(self):

    grade_cutoffs = self.course_data.course.grade_cutoffs
    self.percent = self._compute_percent(self.grader_result)
    self.letter_grade = self._compute_letter_grade(grade_cutoffs, self.percent)
    self.passed = self._compute_passed(grade_cutoffs, self.percent)
