Project: a marks tracker

What you will be able to do

After this lesson you can

• plan a report from a list of data,
• build a program in small steps that each give a result you can check,
• test a program with a small list whose answers you know, and
• extend it with ideas of your own.

The goal

A teacher has the names and the marks of five students. The teacher wants a report with

1. the number of students, the total and the average,
2. the highest mark, and who got it, and the lowest, and who got it,
3. the list of the students who passed (60 or more) and how many they are,
4. the marks from the highest to the lowest.

Step 1: write the answers first

A small list helps. We use five students, and work out the answers by hand.

• The total is 72 + 85 + 64 + 90 + 58 = 369, and the average is 369 divided by 5, which is 73.8.
• The highest is 90 (Kabir). The lowest is 58 (Ana).
• Four students passed: Asha, Ravi, Meera and Kabir.
• From the highest: 90, 85, 72, 64, 58.

These are the answers that the program must give.

Step 2: the program

Step 3: test with a different list

A program that works for one list may be wrong for another. Change the data, work out the answers by hand first, and compare. Test these cases.

• Two students with the same highest mark. What does index give? It gives the first one.
• A list with one student. Highest and lowest are the same student.
• Nobody passed. The list of the passed is empty. Does the program still work?

Set the pass mark above 90. Nobody passes, and the list passed stays empty: [].

Step 4: extend it

Pick one or two, and do them without looking at a solution. Test after each one.

1. A grade for each student. Use an if, elif, else ladder inside the loop, and print name, mark, grade.
2. The failed list. Make a list of those below 60, and show the count.
3. A new student. Use append on both lists, and show that the report changes.
4. Above the average. List the students whose mark is more than the average.
5. A curve. Add 5 marks to everyone, with a maximum of 100. Build a new list, and do not change the original.

Common mistakes

• Changing the order of one list only. names and marks stop matching. Never sort() one of two paired lists. Use sorted() for a copy.
• Dividing by len(names) when the lists differ in length. Keep them the same length.
• Testing only the example. Try one student, and nobody passing.
• Forgetting that index finds the first match only.

Practice

Start with two quick questions. Each New numbers gives you a fresh one, so you can practise as long as you like.

Then the labs and the problems:

1. Warm-up. Open the lab Project: the marks tracker. The checker runs your program on a list of marks that is different from the example.
2. Build. Do Step 4 for one or two extensions.
3. Stretch. Open the problem Remove the repeats again, and make a list of the different marks in the class.

Remember these

• Work out the answers by hand first. Then write the program, and compare.
• Two lists in the same order are read together by position.
• Use sorted() when you must keep the original order.
• Test the edges: one item, no items, ties.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Why do we use sorted() and not sort() in the tracker?

2. What does marks.index(max(marks)) give?

3. What does the tracker show for the list of the passed, if nobody passed?