我正在尝试了解实例属性与类属性和属性之间的区别。我有下面的代码，我想区分这些因素。

class Student:
    firstname = ""
    lastname = ""
    ucid = ""
    department = ""
    nationality = ""
    courses = {}

    def __init__(self, fname, lname, ucid, dept, n):
        self.firstname = fname
        self.lastname = lname
        self.ucid = ucid
        self.department = dept
        self.nationality = n
        self.courses = {}

    def setName(self, fname, lname):
        self.firstname = fname
        self.lastname = lname

    def setDepartment(self, d):
        self.department = d

    def setUcid(self, u):
        self.ucid = u

    def setNationality(self, n):
        self.nationality = n

    def addCourse(self, coursename, gpa):
        self.courses[coursename] = gpa

    def printAll(self):
        print("The name of the student is ", self.firstname, self.lastname)
        print("nationality and UCID: ", self.nationality, self.ucid)
        print("Department: ", self.department)
        print("Result: ")
        for key in self.courses.keys():
            print(key, self.courses[key])

        print("--------------------\n")

s1=Student("Beth","Bean","30303","Computer Science","International")
s1.addCourse("SCIENCE",3.75)
s1.printAll()
s2=Student("Mac","Miller","30303","Envr Science","American")
s2.addCourse("MATH",4.00)
s2.printAll()

从我了解的属性将是：firstname,lastname,ucid,department,nationality,courses 但我不知道什么instance attributes和class attributes会。