Python script to calculate GPA for any semester or overall in college

GPA Calculator/gpa_calculator.py

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+class GPACalculator:
+    def __init__(self, number_of_courses):
+        self.is_valid_grade = True
+        self.course_grades = []
+        self.number_of_courses = number_of_courses
+        self.if_invalid_grade = ""
+
+    def grade_validator(self):
+        for i in range(self.number_of_courses):
+            x, y = input(f"Course {i+1} grade: "), int(input(f"Credits for course {i+1}: "))
+            self.course_grades.append((x.upper(), y))
+            print()
+        for x in self.course_grades:
+            if x[0].upper() not in GRADE_TO_GP:
+                self.if_invalid_grade = f"{x[0].upper()} is not a valid grade!"
+                self.is_valid_grade = False
+                return self.is_valid_grade
+        return self.is_valid_grade
+
+    def overall_gpa_using_previous(self):
+        if self.grade_validator():
+            current_gpa = float(input("Current overall GPA: "))
+            print()
+            credits_completed_till_now = int(input("Total credits completed till now: "))
+            print()
+            current_sem_product = 0
+            total_credits = 0
+            for grade, credits in self.course_grades:
+                current_sem_product += credits*GRADE_TO_GP[grade]
+                total_credits += credits
+            return f"Expected Overall GPA after the current semester: {round((current_sem_product + (current_gpa * credits_completed_till_now))/(total_credits + credits_completed_till_now), 2)}"
+        else: return self.if_invalid_grade
+
+    def overall_gpa(self):
+        if self.grade_validator():
+            product = 0
+            total_credits = 0
+            for i, j in self.course_grades:
+                product += j*GRADE_TO_GP[i]
+                total_credits += j
+            return f"Expected Overall GPA: {round(product/total_credits, 2)}"
+        else: return self.if_invalid_grade
+
+if __name__ == "__main__":
+    GRADE_TO_GP = {
+    "A" : 4,
+    "A-" : 3.67,
+    "B+" : 3.33,
+    "B" : 3,
+    "B-" : 2.67,
+    "C+" : 2.33,
+    "C" : 2,
+    "F" : 0
+}
+
+    while True:
+        choice = input("\n*** GPA Calculator ***\n\n1. Calcualte expected GPA after the current semester\n2. Calculate the GPA using each course's grade\n3. Press 'q' to quit\n\nYour choice number: ")
+        print()
+        try:
+            if choice == "1":
+                number_of_courses = int(input("Number of courses taken in the current semester: "))
+                new_gpa = GPACalculator(number_of_courses)
+                print(new_gpa.overall_gpa_using_previous())
+            elif choice == "2":
+                number_of_courses = int(input("Number of courses taken: "))
+                new_gpa = GPACalculator(number_of_courses)
+                print(new_gpa.overall_gpa())
+            elif choice.lower() == "q" or choice == "3":
+                print("Goodbye!")
+                x = input("Press enter to exit...\n")
+                break
+            else:
+                print("Enter a valid choice number!")
+                continue
+        except Exception as e:
+            print("\nInvalid input!")