Wanted: Advice from CS teachers

[petealexharris@mastodon.scot]

@futurebird @wakame

The thing I keep saying is: an error message is not a person telling you what specifically went wrong this time. It's a string somebody writing the program months or years ago thought would describe what they *guessed* back then might cause the code to reach that state unexpectedly.

1. Code can always be wrong, sometimes in ways the programmer hadn't thought of (in fact often since they probably handled the ways they'd thought of) and,
2. Error handling code is code.

[nini@oldbytes.space]

@futurebird When the computer doesn't do the thing when it's supposed to it can be like "why isn't the machine doing what I say?", they're not the source of the issue but the computer can be. When you're the computer, you only have yourself to fix the problem.

[recyclist@toot.community]

@futurebird Maybe a change of emphasis focussing on "getting it working" as the task, while entering the code becomes a more mechanical step that just has to be done?

[paco@infosec.exchange]

@futurebird I’m pivoting off this just to share a funny story. An old CS prof shared this with me when I was staff in a CS department at a university.

One of his undergrads had come to him with a big printed listing of their code (back when that was how you did that! It was probably FORTRAN printed on fan-fold paper). They obviously wanted him to find the problem in their code. It became clear quickly that they hadn’t done anything to debug it themselves.

He started point at various places in the listing. “Right here, add PRINT ‘I am a dumbass’. And here: PRINT ‘I am a dumbass’” and so on. “Then run it and see how many dumbasses you get.”

Now, did he really do that? Is that just how he tells the story? Who knows. But it’s funny. And anyone who has ever written code will agree that this works sometimes.

[futurebird@sauropods.win]

@petealexharris @wakame

"Error handling code is code."

It had not occurred to me that a student might not see it that way "some guy wrote code to try to tell you what went wrong" but I can see how this might not be how a student might see the errors.

It's like when I realized as a kid that all books are just ... written by people. A revelation. I think I thought, on some level, books were a natural product of the universe. When I realized they could have typos, bad ideas it was so exciting.

[futurebird@sauropods.win]

@paco

My students are too hard working and sensitive to deserve such things.

But.

Well, I have met other people in my life.

[zwifi@framapiaf.org]

@futurebird a teacher of mine had a nice trick for this, that I reused when teaching: he would reply "I won't help you until you have drawings of what the code should do, and comments everywhere". Having the students make diagrams (if they didn't start there) helped them find architectural issues in the code logic, and writing comments had them be their own rubber ducks, and forced them to re-read things. In a lot of cases, they figured the issue out before being ready to call ^^.

[futurebird@sauropods.win]

@Zwifi

I do this with my older students and with those with more experience. This is the one course that I teach that EVERYONE must take. So there are kids there who have never programmed anything. Kids who were confused when I had them use a computer with a mouse since they'd never seen one in person before.

I'm glad we have such a course. But they just don't know enough to do this yet.

And I have an agenda: I want them to have fun.

[pitmutt@gts.zebras.social]

@futurebird @wakame I am in my 40s and I still, occasionally, spend hours trying to fix line 32.

[fortunos@monads.online]

@futurebird my student tutor had an annoying habit of answering questions like that with "try doing it right instead of wrong", which was pretty obviously just a way to not get flooded with this exact type of comment.

On the one hand, it's smarmy and unhelpful. On the other hand, sometimes it's useful to tell someone to sit down and not panic in your face so you can continue doing your thing (for their benefit)

[mcduncanlab@mstdn.social]

@futurebird

Thanks this is really helpful. We teach a graduate class on quantitative cell biology based in python. Many ppl don’t have prior coding experience, we probably need a section like this.

[jgrg@mstdn.science]

@futurebird This is what I would have suggested. Introduce the compiler, explain that you will encounter errors, but the error messages are designed to be as helpful as they can be.

(If you're using Python, error messages have been worked on over the last few major releases, with teaching particularly in mind, so it's worth using the most recent.)

[pete@mas.to]

@futurebird

Test Driven Development can help, although there are skills needed, and you can have errors in your tests!

But the skills needed to write/troubleshoot a good test are more focused/limited than being able to code

Tests also encourage you to write testable code, which is usually modular/functional, and broken code elsewhere is less likely to affect it.

Monolithic code is hard to test/debug.

[paco@infosec.exchange]

@futurebird Of course. I wouldn’t ever say that to someone trying to learn. But you could tell them the story about the grumpy professor who was a jerk, and they can laugh while learning what printf() debugging is. 😀

[wakame@tech.lgbt]

@futurebird @petealexharris

Same with the "average end user":
Your text processor or spreadsheet program also never says "This is the developer writing: I have no idea what you just did, but I didn't expect this."

Only "Error 0x8002f0f0: Good luck trying to find out what that means."

[lappenjammerdiezweite@social.vivaldi.net]

@futurebird Can I just say: reading this makes me aware what a great teacher you are. Your overall approach and your thoughts about finding the bugs are inspirational. Also they demonstrate in themselves how to try and find the error that causes your students to act differently to their standard.

[az@post.lurk.org]

@futurebird caveat: Not a teacher!

I'm not sure what level your students are at, what specifically you are teaching them or how much control you have over the course but...

If you've not seen it already you might like to look at https://hedy.org . It's a language designed for teaching that gradually adds syntax as you explore concepts until you reach a subset of syntactically valid Python. The error messages are also very useful, thoughtfully designed and tested in classroom settings.

Excellent talk by the creator here www.youtube.com/watch?v=6ED36HvQSvk

Honorable mention to Elm and Rust for having excellent error messages too!

[catselbow@fosstodon.org]

@futurebird

Also: If you see pages and pages of errors, start by looking at the first error message. Often, that's the cause of all the others. Students sometimes just give up when confronted with a wall of errors.

[jhavok@mstdn.party]

@futurebird I guess this was an advantage of punch cards for teachers. We had to take our deck down to the mainframe and put it in the queue to find out if it ran, then figure out why it didn't on our own.

Maybe try having the students debug for themselves instead of begging for handholding.

[willyyam@mastodon.social]

@futurebird @wakame The metaphor I use with line numbers in error messages is "I fell down on line 32. I don't know where I tripped, but this is where I fell."

It is a hint, and you can find it from there, but the cause could be before. Students understand that tripping and falling are distinct, causal actions, and that knowing what you tripped on may be unknowable until you go back and look.