Project 2: a quiz

What you will be able to do

After this lesson you can

• keep related data in two lists that match by position,
• loop over the positions to ask each question,
• compare a reply with an answer in a way that forgives capitals and spaces,
• work out a percentage, and
• test the comparison before the quiz.

The plan

A quiz needs four things: questions, answers, a way to ask, and a score.

• Keep the questions in one list and the answers in another. The same position belongs together: question 0 goes with answer 0.
• Use a loop to go through the positions. In each round: ask, compare, and add to the score.
• At the end, work out the percentage.

Work out the expected result first. The four questions of our quiz have the answers paris, 7, 144 and mars. If a student answers Paris, 7, 150 and Mars, three are right: 3 out of 4, which is 75 percent.

Step 1: the thinking, in functions

The most delicate part is comparing a reply with an answer. A student may type Paris, PARIS or paris . All three are right. The comparison must forgive capitals and spaces at the ends. It is a job for a small function, and we can test it before we build the quiz.

Step 2: the quiz

Type four answers in the Input box, one on each line, for example Paris, 7, 144 and Mars, and press Run. Then type wrong answers, and see the other message.

• for i in range(len(questions)): goes through the positions 0, 1, 2 and 3.
• questions[i] and answers[i] are the matching pair.
• score is a counter. It starts at 0, and 1 is added for each correct reply.
• At the end, the percentage is worked out by the function.

Python rounds a half to the even neighbour, so 87.5 percent shows as 88 and 62.5 percent as 62.

A typical mistake

What if you add a question to questions and forget to add its answer to answers?

Step 3: test

Test the function with the cases that matter: the right answer in a different style, a wrong answer, an empty reply, and a reply with spaces inside. Test the percentage for 0, for all right, and for a part.

Step 4: extend it

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

1. More questions. Make a quiz about your favourite subject. Remember to keep the lists the same length.
2. A message from the percentage. Under 50: Keep practising. 50 to 79: Good. 80 and more: Excellent. This is a decision ladder, so test its edges.
3. Two correct spellings. Let an answer such as 7 also accept seven. A list of allowed answers for each question is one way.
4. Shuffle the questions. random.shuffle() mixes a list. But the answers must be shuffled in the same way, so think about how to keep the pairs together.

Common mistakes

• Lists of different lengths. An IndexError.
• Comparing without lower() and strip(). The student who types Paris loses a mark.
• Dividing by the wrong number. The total is len(questions).
• Putting input() in the function that compares. You cannot test it.

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 Quiz marker. You write the function that marks one answer and the one that counts the score, and the checker tries both.
2. Build. Open the problem Add a question and the problem Capital letters in the reply.
3. Stretch. Open the problem A message from the percentage and test its edges.

Remember these

• Two lists in the same order work like a table: the same position, the same question and answer.
• for i in range(len(a_list)) goes through the positions.
• Clean the reply with lower() and strip() before you compare. Put the comparison in a function and test it.
• The lists must be the same length.

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 the percentage if a student scores 3 out of 4?

2. Why must the two lists have the same length?

3. Why do we test is_correct before building the quiz?