在python中更改嵌套字典值

Question

I have a dictionary, who's keys are student ID #'s and the values are another dictionary. The nested dictionary has keys that state the type of assignment, and the values are the grades for the assignment, in a list.

So I'm trying to change the list of grades for each assignment (to drop lowest grade, average them, etc.), but I can't figure out a way to pick them out of the dictionary in the first place.

Here's what part of the dictionary looks like:

D = {"123-45-6789":{"hw":[98,89,92,75], "quiz":[45,36,42,50,29,27,40,41], "exam":[175,157]}, "534-77-9326":{"hw":[67,89,55,78], "quiz":[78,45,67,23,45,78,88,91], "exam":[187,146]},   ....... etc.

Any help will be very appreciated.

***and I forgot to mention that I planned on iterating through the dictionary to edit each list of grades, because there are many student ID #'s. So I guess what I'm really asking is: What would the syntax look like to refer to each student ID #, then each list of grades for every ID #

Answer 1

You can get the list in the dictionary using assignment expression:

lst = students_grades_dictionary["123-45-6789"]["hw"]

You can remove a grade from the list by using the pop function:

lst.pop(<grade index>)

Since lst is a reference to the grade list, any changes you made to it will also change the grade list in the dictionary.

Answer 2

You can use a mixture of list.remove and min() after finding the length of the list.

max_size = 4
new_score = 87
hw_list = data[student_id]['hw']

if len(hw_list) >= max_size - 1:
    hw_list.remove(min(hw_list))

hw_list.append(new_score)

Note this will not handle if the list is already more than 2 items larger than the specified max len but this will get you started.