class Gradebook:
    def __init__(self):
        self.students = {}

    def get_best_exam_student(self, subject):
        semestr = sorted(self.students, key=lambda name: self.students[name].get(subject, {}).get('semestr', 0))
        return semestr[-1]

    def get_passed_exams(self):
        return set(subject for subjects in self.students.values() for subject in subjects)

    def print_result_grades(self):
        for name in self.students:
            print(name, ' '.join('{}-{}'.format(n, round(rate['exam']*.3 + rate['semestr']*.7))
                                 for n, rate in self.students[name].items()))

# заполнить тест данными
from random import randrange
G = Gradebook()
student_count = 3
subjects_count = 4
max_rate = 12
_subjects = ['subject%s' % n for n in range(subjects_count)]
for name in [('Name%s' % n, 'Surname%s' % n) for n in range(student_count)]:
    G.students[name] = student = {}
    for r in range(randrange(5)):
        subject = _subjects[randrange(subjects_count)]
        rate = dict(exam=randrange(max_rate), semestr=randrange(max_rate))
        student[subject] = rate
print('n'.join(map(str, G.students.items())))

# проверить
print(G.get_best_exam_student('subject1'))
print(G.get_passed_exams())
G.print_result_grades()

(('name-1', 'surname-1'), {'subject-1': [0, 1]})
(('name-0', 'surname-0'), {'subject-0': [7, 0], 'subject-1': [2, 4], 'subject-3': [8, 10]})
(('name-2', 'surname-2'), {'subject-0': [8, 8], 'subject-2': [2, 11], 'subject-3': [0, 10]})
**********
('name-0', 'surname-0')
**********
{'subject-0', 'subject-2', 'subject-1', 'subject-3'}
**********
 surname-1 subject-1=1
 surname-0 subject-0=2 subject-1=3 subject-3=9
 surname-2 subject-0=8 subject-2=8 subject-3=7