Chciałbym iterować słownik obiektów w sposób posortowany

<code>import operator

class Student:
        def __init__(self, name, grade, age):
                self.name = name
                self.grade = grade
                self.age = age


studi1=Student('john', 'A', 15)
studi2=Student('dave', 'B', 10)
studi3=Student('jane', 'B', 12)

student_Dict = {}
student_Dict[studi1.name]=studi1
student_Dict[studi2.name]=studi2
student_Dict[studi3.name]=studi3

for key in (sorted(student_Dict, key=operator.attrgetter('age'))):
    print(key)
</code>

Daje mi to komunikat eror: „AttributeError: obiekt„ str ”nie ma atrybutu„ age ””