扩展时的字典KeyError

Question

I'm trying to extend the dictionary when a user completes the quiz. I'm looking to store the last three scores only for a user but I get an KeyError when I try to add it to the empty dictionary and a unhashable list error when I try to implement the score as a list.

studentScores = {}

def quiz():
    print("WELCOME TO THE MATH QUIZ\n")
    global student
    student = input("What is your name? ")
    global classname
    classname = input("Which class are you in? (1, 2, 3) ")
    global score
    score = 0

def addDict():
    global student
    global classname
    global score
    score = str(score)
    studentScores[student + classname, score]
    print(studentScores)

Answer 1

As noted in comments, the problem is on this line:

studentScores[student + classname, score]

What this line does: It creates a tuple of (student + classname, score) and uses that tuple as a key to the dictionary. And since that key does not exist, it raises an exception.

>>> student = "foo"
>>> classname = "bar"
>>> score = 0
>>> studentScores = {}
>>> studentScores[student + classname, score]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: ('foobar', 0)

Instead, you want to use just student + classname as the key and assign to it the value of score .

>>> studentScores[student + classname] = score
>>> studentScores
>>> {'foobar': 0}