Project 3: a grade book

What you will be able to do

After this lesson you can

• turn two lists into a neat report,
• keep the thinking in small functions,
• line up the columns of a table with an f-string,
• find the name that belongs to the highest mark, and
• count how many items fall into each group.

The plan

A grade book turns raw marks into a report.

1. The data. Names and marks in two lists, with the same position for the same student.
2. The functions. grade(mark) gives a letter. average(numbers) gives an average. Small functions are easy to test.
3. The report. A loop prints a line for every student. Then the class average and the highest mark are shown.

Write the expected answers first. For the five students Asha 72, Ravi 85, Meera 64, Kabir 90 and Ana 58: the grades are C, B, C, A and D (90 and more is A, 75 and more is B, 60 and more is C, and below 60 is D). The average is 369 divided by 5, which is 73.8. The highest mark is 90, by Kabir.

The program

Test the grade function

The edges of the grade function are 60, 75 and 90. Write a table of cases, and run a loop, as you learned in the course on functions.

If a student with exactly 75 gets a C, the fault is at the edge mark >= 75, and the table finds it at once.

A new pattern: counting by group

A teacher wants to know how many students got each grade. This is a counting job with four counters. A neat way is a list of the letters, and a list of counts at the same positions.

The four bars always add up to 5, because every mark lands in exactly one group.

Extend it

Pick one or two, and do them without looking at a solution. Write the expected answers first.

1. The students below 60. Make a list of their names and show how many they are.
2. Sort the report from the highest mark to the lowest. (Careful: the names must move with the marks. Think about how to keep the pairs together. A list of pairs is one way.)
3. A new student. Use append on both lists, and show that the report changes.
4. The median. The middle mark when the marks are in order.
5. A letter for the class. Is the class average a B? Use grade(average(marks)).

Common mistakes

• Lists of different lengths. An IndexError.
• Sorting only the marks. The names no longer match.
• < and > mixed up in the f-string widths. < is left, > is right.
• No test for the edges of the grade. The students at 60, 75 and 90 are the ones who find the faults.
• Putting print in the functions. You cannot use their answers.

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 Grade book report. You write the grade function and the counting, and the checker tries them on a list that is different from the example.
2. Build. Open the problem Who has the highest mark? and the problem An average function.
3. Stretch. Open the problem Who passed? and then list the students who are above the class average.

Remember these

• Lists of the same length, in the same order, are read together by position.
• Put each job in a small function, and test the functions at their edges.
• a_list.index(value) gives the position of a value.
• Count by group with a list of the groups and a list of the counts at the same positions.

Check yourself

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

1. What is grade(85) in the grade book above?

2. What does marks.index(90) give for [72, 85, 64, 90, 58]?

3. What does {x:>4} do in an f-string?