Q.For the SMIS System given in Chapter 3, let us do the following:
Write a program to take in the roll number, name and percentage of marks for n students of Class X and do the following:
• Accept details of the n students (n is the number of students).
• Search details of a particular student on the basis of roll number and display result.
• Display the result of all the students.
• Find the topper amongst them.
• Find the subject toppers amongst them.
(Hint: Use Dictionary, where the key can be roll number and the value an immutable data type containing name and percentage.)

Use a dictionary keyed by roll number whose value is an immutable tuple (name, marks_tuple, percentage) — per-subject marks are needed because the question also asks for subject toppers. Search is a direct students[roll] lookup, display-all loops over students.items(), and both topper questions are one-liners with max(..., key=...). …

Concept first — why a dictionary, and why an immutable value?

A student record must be looked up by roll number. A list would force us to scan every element; a dictionary maps roll number → details directly, so roll in students and students[roll] are instant. The hint asks for an immutable value so a record cannot be accidentally modified in place — a tuple is exactly that.

One design note (stated openly): the stem stores only percentage, yet also asks for subject toppers — which is impossible without per-subject marks. So the record we store is

students[roll] = (name, marks_tuple, percentage) — still one immutable tuple, but now rich enough to answer every requirement.

The program

SUBJECTS = ("English", "Maths", "Science", "Social Science", "IT")

def accept_details():
    """Accept details of n students into a dictionary keyed by roll number."""
    students = {}
    n = int(input("How many students in Class X? "))
    for i in range(n):
        print(f"\n-- Student {i + 1} --")
        roll = int(input("Roll number : "))
        name = input("Name        : ")
        marks = tuple(float(input(f"Marks in {sub} (out of 100): "))
                      for sub in SUBJECTS)
        percentage = round(sum(marks) / len(SUBJECTS), 2)
        students[roll] = (name, marks, percentage)   # value = immutable tuple
    return students

def search_student(students):
    roll = int(input("Enter roll number to search: "))
    if roll in students:                              # O(1) membership test
        name, marks, pct = students[roll]
        print(f"Roll {roll}: {name}  |  Percentage: {pct}%")
    else:
        print(f"No student with roll number {roll}.")

def display_all(students):
    print(f"\n{'Roll':<6}{'Name':<12}{'Percentage':>12}")
    for roll, (name, marks, pct) in students.items():
        print(f"{roll:<6}{name:<12}{pct:>11}%")

def find_topper(students):
    top = max(students, key=lambda r: students[r][2])  # compare percentages
    name, _, pct = students[top]
    print(f"Topper: {name} (Roll {top}) with {pct}%")

def subject_toppers(students):
    for i, sub in enumerate(SUBJECTS):
        top = max(students, key=lambda r: students[r][1][i])
        name, marks, _ = students[top]
        print(f"{sub:<15}: {name} (Roll {top}) with {marks[i]} marks")

def main():
    students = accept_details()
    while True:
        print("\n1. Search by roll number\n2. Display all results"
              "\n3. Class topper\n4. Subject toppers\n5. Exit")
        choice = input("Enter choice (1-5): ")
        if choice == "1":
            search_student(students)
        elif choice == "2":
            display_all(students)
        elif choice == "3":
            find_topper(students)
        elif choice == "4":
            subject_toppers(students)
        elif choice == "5":
            print("Goodbye!")
            break
        else:
            print("Invalid choice — enter 1 to 5.")

main()

Expected output (sample run with 2 students)

How many students in Class X? 2

-- Student 1 --
Roll number : 101
Name        : Asha
Marks in English (out of 100): 82
Marks in Maths (out of 100): 95
Marks in Science (out of 100): 88
Marks in Social Science (out of 100): 79
Marks in IT (out of 100): 91

-- Student 2 --
Roll number : 102
Name        : Ravi
Marks in English (out of 100): 90
Marks in Maths (out of 100): 84
Marks in Science (out of 100): 92
Marks in Social Science (out of 100): 85
Marks in IT (out of 100): 88

1. Search by roll number
2. Display all results
3. Class topper
4. Subject toppers
5. Exit
Enter choice (1-5): 2

Roll  Name          Percentage …