Lists Mini Project — Grade Book

What you're building

A grade book for three subjects: Math, English, Biology.

The user adds grades for each subject. The program calculates and displays the average per subject and the overall average.

What you need to know first

• Nested lists
• append()
• sum() and len()
• for loops
• if / elif / else
• while True with break
• input() and float()

The brief

Build a program that:

• Stores grades in a nested list — one inner list per subject
• Shows a menu: 1 — Math, 2 — English, 3 — Biology, 4 — Show averages, 5 — Quit
• Adds the grade to the correct subject list
• On option 4 — prints the average for each subject and the overall average
• Handles the case where a subject has no grades yet

Think before you code

• How do you map menu choices 1, 2, 3 to the correct inner list?
• How do you calculate an average from a list of numbers?
• What do you do if a subject list is empty when the user asks for averages?
• How do you calculate the overall average across all subjects?

Your starting point

subjects = ["Math", "English", "Biology"]
grades = [[], [], []]

while True:
    print("\n1 — Add Math grade")
    print("2 — Add English grade")
    print("3 — Add Biology grade")
    print("4 — Show averages")
    print("5 — Quit")
    choice = input("Your choice: ")

    # your code here

Expected output

1 — Add Math grade
2 — Add English grade
3 — Add Biology grade
4 — Show averages
5 — Quit
Your choice: 1
Math grade: 8.5
Added.

Your choice: 1
Math grade: 9
Added.

Your choice: 2
English grade: 7
Added.

Your choice: 4

Math:    average 8.75
English: average 7.00
Biology: no grades yet.

Overall average: 7.92

Your choice: 5
Done. Out.

Heads up!

• Grades come in as strings from input() — convert with float()
• Use the menu choice as an index into grades — choice "1" maps to grades[0]
• Check len() before dividing — an empty list causes a ZeroDivisionError
• For the overall average, flatten all grades into one list or sum totals and counts separately

The solution

subjects = ["Math", "English", "Biology"]
grades = [[], [], []]

while True:
    print("\n1 — Add Math grade")
    print("2 — Add English grade")
    print("3 — Add Biology grade")
    print("4 — Show averages")
    print("5 — Quit")
    choice = input("Your choice: ")

    if choice in ("1", "2", "3"):
        index = int(choice) - 1
        grade = float(input(f"{subjects[index]} grade: "))
        grades[index].append(grade)
        print("Added.")

    elif choice == "4":
        print()
        total_sum = 0
        total_count = 0
        for i in range(len(subjects)):
            if len(grades[i]) == 0:
                print(f"{subjects[i]:8} no grades yet.")
            else:
                avg = sum(grades[i]) / len(grades[i])
                print(f"{subjects[i]:8} average {avg:.2f}")
                total_sum += sum(grades[i])
                total_count += len(grades[i])
        if total_count > 0:
            print(f"\nOverall average: {total_sum / total_count:.2f}")

    elif choice == "5":
        print("Done. Out.")
        break

    else:
        print("Invalid choice. Enter 1 to 5.")