edited class subject and grade

subject.py

@@ -20,6 +20,17 @@ class Subject:
     def return_grade_categories(self):
         return [i for i in self.grades]
 
+    def return_average_of_category(self, category):
+        return sum(self.grades[category][0]) / len(self.grades[category][0])
+
+    def return_average_of_subject(self):
+        rating_sum = 0
+        grade_sum = 0
+        for i in self.grades:
+            rating_sum += self.grades[i][1]
+            grade_sum += self.return_average_of_category(i)
+        return grade_sum / rating_sum
+
 
 class Grade:
     def __init__(self, grade, name, date=str(str_date.now())):