from statistics import mean


def calculate_average_grades(assignments):
    """The order for this method is O(N^2)
    We have one iteration of N elements and another one but with a iteration of N inside
    'grades = {}' -> O(1)
    'for assignment in assignments' -> O(N)
    'student = assignment.student.name' -> O(1)
    'grades[student]' -> O(1)
    'grades[student] = []' -> O(1)
    'grades[student].append(assignment.grade)' -> O(1)
    'for student in grades:'
    '    grades[student] = mean(grades[student])' -> O(N^2)
    5*O(1) + O(N^2) + O(N), MAX(O(N), O(N^2)) = O(N^2)
    """
    grades = {}

    for assignment in assignments:
        student = assignment.student.name
        try:
            grades[student]
        except KeyError:
            grades[student] = []
        finally:
            grades[student].append(assignment.grade)

    for student in grades:
        grades[student] = mean(grades[student])

    return grades