Is it possible to create nested class attributes?

I’m pretty new to Python and have recently learned about classes. I’ve been experimenting around with them and have come up with a student/course grading system. Here’s the code so far:

class course:
    TOTAL_COURSES = 0

    def __init__(self, name, room, max_students):
        self.name = name
        self.room = room
        self.max_students = max_students
        self.student_list = []
        course.TOTAL_COURSES += 1
 
    def addStudent(self, student):
        # Checks if the class is below max capacity
        if len(self.student_list) < self.max_students:
            self.student_list.append(student)
            # Adds the course to the student's course list
            student.course_list.append(self)
            return True
        return False

So this creates a course class, which I can add students to and set their rooms and other stuff. I’ve got another class, which is intended to store information on students:

class student:
    TOTAL_STUDENTS = 0

    def __init__(self, name, age, gender):
        self.name = name
        self.age = age
        self.gender = gender
        # Courses in course_list are stored as objects
        self.course_list = []
        student.TOTAL_STUDENTS += 1

Pretty simple; I’ve just been stuck on how to create the actual grading system. If I were to do:

s1 = student("Tom", 17, "Male")
c1 = course("English", "E123", 25)

Would it be possible to then use “nested attributes”? So I’d assign that student’s grade of a course to a value like:

s1.c1.grade = "A+"

This however doesn’t work, and throws an (expected) AttributeError. So would I have to use my previously created course_list?

s1.course_list[0].grade = "A+"

Even then I’m not sure how I’d assign grade to that course object.

Answer

Here’s a solution that addresses some of the above issues by assigning a “course slot” to a student, rather than the course itself. As you might imagine, there is a limit to the number of course slots available which depends on the course max size. The code can be developed a lot further, but I thought this could be good to get you started:

class Student:

    def __init__(self, name, age, gender):
        self.name = name
        self.age = age
        self.gender = gender
        self.courses = {}
        
    def addCourse(self, course):
        if course.status=='Enrolled':
            self.courses[course.name] = course
        else:
            self.courses[course.name] = course.status

            
class Course:

    def __init__(self, name, room, max_students):
        self.name = name
        self.room = room
        self.max_students = max_students
        self.student_list = []
        
        self.course_slots_filled = 0
        self.course_slots_available = max_students
        
    def __str__(self):
        return 'Course_object_{}'.format(self.name)
 
    def check_slots_available(self):
        if self.course_slots_filled < self.max_students:
            return True
        else:
            return False
    
    class CourseSlot:
        def __init__(self, name, student_name, status):
            self.name = name
            self.student_name = student_name
            self.status = status
            self.grade = 'No grade assigned'
        
        def __repr__(self):
            return 'CourseSlot_object_{}'.format(self.name)
        
        def set_grade(self, grade):
            self.grade = grade
            
    
    def assign_course_slot(self, student_name):
        if self.check_slots_available():
            self.course_slots_filled+=1
            self.course_slots_available-=1
            status = 'Enrolled'
            self.student_list.append(student_name)
        else:
            print('Sorry, {} class is full! {} not enrolled.'.format(self.name, student_name))
            status = 'Not enrolled'
            
        return self.CourseSlot(self.name, student_name, status)

Example usage

Instantiate courses:

physics = Course('Physics','101',5)
chemistry = Course('Chemistry','102',1)

Instantiate student 1 and assign a course slot:

s1 = Student("Tom", 17, "Male")
s1.addCourse(physics.assign_course_slot(s1.name))
s1.addCourse(chemistry.assign_course_slot(s1.name))
s1.courses['Physics'].set_grade('A+')

[v for v in s1.courses.values()]

# >>> [CourseSlot_object_Physics, CourseSlot_object_Chemistry]

Instantiate student 2 and assign a course slot

s2 = Student("Susan", 18, "Female")
s2.addCourse(physics.assign_course_slot(s2.name))
s2.addCourse(chemistry.assign_course_slot(s2.name))

#>>> Sorry, Chemistry class is full! Susan not enrolled.

Get course info:

print('Physics course slots filled: ',physics.course_slots_filled)
print('Physics course slots available: ',physics.course_slots_available)
print('Chemistry course slots filled: ',chemistry.course_slots_filled)
print('Chemistry course slots available: ',chemistry.course_slots_available)

#>>> Physics course slots filled:  2
#    Physics course slots available:  3
#    Chemistry course slots filled:  1
#    Chemistry course slots available:  0

print('Physics student list: ',physics.student_list)
print('Chemistry student list: ',chemistry.student_list)

# >>> Physics student list:  ['Tom', 'Susan']
#     Chemistry student list:  ['Tom']

for s in [s1,s2]:
    for c in s.courses.values():
        try:
            print('{} {} grade: {}'.format(s.name, c.name, c.grade))
        except AttributeError:
            pass

# >>> Tom Physics grade: A+
#     Tom Chemistry grade: No grade assigned
#     Susan Physics grade: No grade assigned

I guess the cheat is that the course student_list only gets the name of the student and not the Student object, which could probably work if you pass it a unique ID and then iterate through a list of Student objects to match on ID. Something to think about anyway.