#MUTABILITY

from typing import List, Optional

class Student:
    def __init__(self, name: str, grades: Optional[List[int]] = None):
        self.name = name 
        self.grades = grades or []

    def take_exam(self, result: int):
        self.grades.append(result)

bob = Student("Bob")
rolf = Student("Rolf")
bob.take_exam(90)
bob.take_exam(85)
bob.take_exam(95)
rolf.take_exam(92)
print(bob.grades)
print(rolf.grades)