class Student():

    def __init__(self,n,m):
        self.sname = n
        self.major = m
        self.courses = []
        self.gpa = 0

    def add_course(self,cnum,credits,grade):
        self.courses.append((cnum,credits,grade))

    def gpa(self):
        points_for_grade = {'A':4,'B':3,'C':2,'D':1,'F':0}
        grade_points = 0
        num_credits = 0
        for course in self.courses:
            num_credits += course[1]
            grade_points += course[1]*points_for_grade[course[2]]
        if num_credits != 0:
            return grade_points/num_credits
        else:
            return None

    def __str__(self):
        return "(" + self.sname + "," + self.major + "," + str(self.courses) + ")"
    

s1 = Student("Jones","CSC")
s2 = Student("Smith","MATH")
s1.add_course("1301",4,"A")
s1.add_course("1302",4,"B")
s1.add_course("2510",4,"C")
s2.add_course("1301",4,"C")
print(s1.gpa())
print(s2.gpa())

3.0
2.0

"abc" + str([10,20,30])

'abc[10, 20, 30]'