Week 8 Lab: Practice Reading

Git Repository: https://classroom.github.com/a/EzhDFihA

You have spend almost all of the lab and studio sessions writing code for this class. Writing code is relatively straightforward – you enter code into the text editor, you run the code, see if it does what you want it to, and then change it until it does. One aspect of this is that you don’t always have to really understand what the code it doing – sometimes you get lucky and it just works.

The goal for today is to practice reading code. Reading code is harder than writing code. Reading code requires you to think more carefully about what each line of a program is doing. It requires you to keep track of what is stored in variables, and what variables contain what information. It requires you to think through options for if statements, to try to understand why they are there.

You are going to practice reading today, to try to get better at doing so. Reading code is one of the best ways to become a better programmer, once you have the basics down. But reading code is a skill that requires practice, just like all other skills.

Note: For TODAY only, you are NOT allowed to use ChatGPT, CoPilot, or any other generative AI system. All code reading must be done yourself.

(Using generative AI for this defeats the purpose of practicing reading code. However, reading code is useful when using generative AI to understand what it outputs and whether it does what it is supposed to.)

Exercise 1: Timer

Start by looking at the file timer_seconds.py. Run it. What does it do?

Open up the code for timer_seconds.py and see how it works.

time.sleep() waits a specified number of seconds. So if you say time.sleep(10), it will wait 10 seconds. If you say time.sleep(20), it will wait 20 seconds.

If you wanted to wait for minutes instead of seconds, how would you do that? Think about how you might want to modify this program if you wanted to ask the user for how many minutes the user wants to wait. Then have the program wait that many minutes. Remember, if you have a number of minutes, you can calculate how many seconds that is by multiplying by 60 (since there are 60 seconds in a minute).

Now look at the program timer.py. Is that how you would have done it?

Check and make sure the timer program works; run it, ask it for a 2 minute timer, wait two minutes, and see if it tells you to stop at the end of that minute.

Code Reading

For each of the following exercises, your goals is not to write code. It is to read the code and write comments. You should not need to modify the code at all. Instead, you will need to read through the code and figure out what it does.

You are going to use the python timer program on the command line. For each exercise, I will give you an amount of time. Set your timer for that amount of time, and then work on reading the code. Only after your timer goes off can you run the code to see what it does. Your first job is to figure out what the code does without running it. After the timer goes off, you can run the code, and then go back to the code and use what you now know about the program to try to figure out how it does it.

As you work, think out loud. You are working with a partner. Think out loud, and work with your partner to try to figure out what the program is doing. You should be spending a LOT of time talking to each other during this lab. One person (the ‘driver’) should pull up the code on their computer, and then both of you can talk about what it is doing and how it is doing it.

As you figure out what the code does, you will need to add comments to the code that describe what is happening. As a reminder, if you put a # symbol in the code, python ignores everything that comes after that symbol (which we call a ‘comment’). For each line of code, add a comment to the code that explains what that line is doing. Do this for each line of code in the program. You are done with the exercise when you have a comment for every line of code, and also an comment at the top describing the program as a whole. Like this:

# Purpose: this program keeps asking the user if they want to stop, and stops when they say so

while True:                                    # Keep looping forever, until "break"
    answer = input("Do you want to stop? ")    # Ask the user if they want to stop, and store the result in answer
    if answer == "yes":                        # Check if what the user typed in is the word "yes", all lowercase
        break                                  # if it is "yes", then break out of the while loop
                                               # End of the loop, go back to the top of the while loop
print("Done looping!")                         # Print message AFTER loop is broken out of to let the user know the break was successful

Remember: 1) Set time; 2) Read code; 3) Add comments; 4) Only after timer goes off, run the program

A couple of points of advice about comments:

Be sure to include a comment at the top of each program describing the “purpose” of the program as a whole. WHY did someone take the time to write this program?
Try to include a comment for every line in the program. Normally, you won’t need so many comments; good code should be easy to understan. But for today, comment every line so we can see you understand what it does
The easiest place to start is by describing what the line does. So fd(50) could be commented at “Moves the turtle forward 50 steps”. But that is also the most useless comment! WHY does the program move the cursor forward? What is it trying to accomplish? Why 50 steps, and not some other number of steps? Your comment should include not just what the code does, but also why it does it and why it does it that way.

Important: As you finish two to three exercises, before you move on to the next one, ask the instructor or one of the TAs to come over and look at your comments to make sure that they aren’t missing anything. This is important; often we will ask you questions that reveal that you might not have fully understood the program.

Hint: Use print

After the timer goes off, if you are still trying to figure out what the program does, you should use print(). Add print() statements to the program and run it again to print out the contents of variables (or lists or dictionaries) so you can see what is stored in them. This will help you think about what the program does and how it works.

Exercise 2

Set your timer for 2 minutes.

Look at the program in ex2.py. Read the code, and write comments for each line of code as described above. What does this program do?

After your timer goes off, you are allowed to run the program to see and help you. But don’t run it before the timer goes off. Try to read the code and figure out what it does before the timer goes off.

Exercise 3

Set your timer for 5 minutes

Look at the program in ex3.py. Read the code, and write comments for each line of code as described above. What does this program do?

As a reminder, every non-blank line of code should have a comment describing what it is doing, and also why that line is needed as part of the program.

Once you are finished with exercises 2 and 3, ask the instructor or one of the TAs to check your comments before moving on.

Exercise 4:

Set your timer for 5 minutes

Look at the program in ex4.py. Read the code, and write comments for each line of code as described above. What does this program do?

Exercise 5:

Set your timer for 5 minutes

Look at the program in ex5.py. Read the code, and write comments for each line of code as described above. What does this program do?

Once you are finished with exercises 4 and 5, ask the instructor or one of the TAs to check your comments before moving on.

Exercise 6:

Set your timer for 8 minutes

Look at the program in ex6.py. Read the code, and write comments for each line of code as described above. What does this program do?

Once you are finished, ask the instructor or one of the TAs to check your comments before moving on.

Exercise 7:

Set your timer for 7 minutes

Look at the program in ex7.py. Read the code, and write comments for each line of code as described above. What does this program do?

Once you are finished, ask the instructor or one of the TAs to check your comments before moving on.

Exercise 8:

Set your timer for 10 minutes

Look at the program in ex8.py. Read the code, and write comments for each line of code as described above. What does this program do?

Once you are finished, ask the instructor or one of the TAs to check your comments before moving on.

Don’t forget to add, commit, and push all of your comments to your git repository.

Challenge: Eliza

Also in the git repository for this week is the Eliza program that you ran the very first week of the semester. Do this same code reading exercise on that program: for each line of the program, put a comment next to it describing what that line does and how it works. Pay particular attention to the responses variable. What is stored in that variable? It is a list. But a list of what? How does that work? How does it get used?