Hoe do I change the values in dictionary?

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Python

dictionary

import pickle
import student


LOOK_UP = 1
ADD = 2
CHANGE = 3
CHANGE_2 = 4
DISPLAY = 5
QUIT = 6

File = 'students.dat'

def main():
    mystudents = load_students()
    add(mystudents)
    look_up(mystudents)
    change_GPA(mystudents)
    change_grade(mystudents)
    print_data(mystudents)

##    choice = 0
##    while choice != QUIT:
##        choice = get_menu_choice()
##        if choice == LOOK_UP:
##            look_up(mystudents)
##
##save_students(mystudents)

def load_students():
    try:
        input_file = open(File, 'rb')
        student_dict = pickle.load(input_file)
        input_file.close()
    except IOError:
        student_dict = {}
    return student_dict


def look_up(mystudents):
    student_ID = input('Enter an ID')
##    try:
##        print(mystudents[student_ID])
##    except KeyError:
##        print('Not found!')
    print(mystudents.get(student_ID, "Not found!"))
    #print(mystudents)

def add(mystudents):
   name = input('Name:')
   student_ID = input('ID:')
   GPA = input('GPA:')
   grade_course = input('Grade:')
   work_time = input('Hours work:')
   entry = student.Student(name,student_ID, GPA, grade_course, work_time)
   if student_ID not in mystudents:
        mystudents[student_ID] = entry
        print('Student added')
   else:
      print('Entry existed')

def change_GPA(mystudents):
    name = input('Enter student name:')
    student_ID = input('Enter an ID')
    if student_ID in mystudents:
        new_GPA = input('Enter new GPA')
        grade = mystudents[student_ID].grade_course
        work = mystudents[student_ID].work_time
        new_student = student.Student(name,student_ID,new_GPA,grade,work)
        mystudents[student_ID] = new_student
        ##mystudents[student_ID].GPA = new_GPA
        ##mystudents[student_ID].GPA = mystudents[student_ID]
##        #entry = student.Student(name,student_ID, new_GPA,grade_course,work_time)
        print(mystudents[student_ID])
        print('Updated')
    else:
        print('Not found!')
        
def change_grade(mystudents):
    student_ID = input('Enter an ID')
    if student_ID in mystudents:
        grade = input('Enter new grade')
        mystudents[student_ID]
##        grade = mystudents[student_ID].grade_course
##        old_GPA = mystudents[student_ID].GPA
##        old_work = mystudents[student_ID].work_time
##        new_student = student.Student(student_ID,old_GPA,grade,old_work)
##        mystudents[student_ID] = new_student
        mystudents[student_ID].grade_course = grade
        print(mystudents[student_ID])
        print('Updated')
    else:
        print('Not found!')

def display_student_info(mystudents[student_ID]):
    print("Name\tI.D. #\t\tGPA\t\tExpected Grade\t\tEmployment")
    print("----------------------------------------------------------")
    for name in mystudents[student_ID]:
        print(name, '\t', getattr(name, "id_number"),
              '\t', getattr(name, "gpa"), '\t', getattr(name, "expected_grade"), '\t', getattr(name, "work_status"))

        
def save_students(mystudents):
    output_file = open(Filename, 'wb')
    pickle.dump(mystudents, output_file)
    output_file.close()

main()

This is what I'm supposed to do but I've been staring at this code for hours.

1. Look up and print the student GPA
2. Add a new student to the class
3. Change the GPA of a student
4. Change the expected grade of a student
5. Print the data of all the students in a tabular format
6. Quit the program

This is the error message

Traceback (most recent call last):
  File "/Users/kimmyyveee/Documents/Computer Science/Lab10.test2.py", line 104, in <module>
    main()
  File "/Users/kimmyyveee/Documents/Computer Science/Lab10.test2.py", line 18, in main
    change_GPA(mystudents)
  File "/Users/kimmyyveee/Documents/Computer Science/Lab10.test2.py", line 67, in change_GPA
    grade = mystudents[student_ID].grade_course
AttributeError: 'Student' object has no attribute 'grade_course'

And that's my class Student.

#student.py

        class Student:
            def __init__(self, name, student_ID,GPA,grade_course,work_time):
                self.__name = name
                self.__student_ID = student_ID
                self.__GPA = GPA
                self.__grade_course = grade_course
                self.__work_time = work_time
        #Mutator
            def set__student_ID(self, student_ID):
                self.__student_ID = student_ID
            def set__GPA(self, GPA):
                self.__GPA = GPA
            def set__grade_course(self, grade_course):
                self.__grade_course = grade_course
            def set__work_time(self, work_time):
                self.__work_time = work_time

        #return values(Acessor)
            def get_student_ID(self):
                return self.__student_ID
            def get_GPA(self):
                return self.__GPA
            def get_grade_course(self):
                return self.__grade_course
            def get_work_time(self):
                return self.__work_time
            
                
            def __str__(self):
                return '\nStudent Name:'+ self.__name+\
                       '\nStudent ID:'+ self.__student_ID+\
                       '\nStudent GPA:'+ self.__GPA+\
                       '\nStudent Expected Grade:'+ self.__grade_course+\
                       '\nStudent Work Time '+ self.__work_time