Errors, exceptions, and reading a stack trace
By the end of today you can read a stack trace from the bottom up, name the line that actually failed, and say whether an error should be caught, allowed to crash, or fixed at its source.
YesterdayOn Day 4 you saw the call stack grow with each function call. A stack trace is that same stack, printed at the moment something broke.
TomorrowTomorrow you turn this into a method, so you can find bugs that do not announce themselves with an exception.
Why this matters
Most people scroll past stack traces looking for something familiar. A trace is a precise report of what happened, and reading it properly turns a ten-minute guess into a ten-second fix.
- Exceptions
- Stack traces
- Error handling
- Failing fast
Learn it
70 minCopy this into Claude or ChatGPT. It quizzes you before it explains anything, which is deliberate. The resources under it are how you check what it told you.
Today's Master Prompt
Free · sign inA prompt written for this day alone: your level, the exact scope, what to leave out, and an instruction to quiz you before it explains anything. Paste it into Claude or ChatGPT and it teaches you today's material.
Check it against something that is not a model
An assistant can be fluent and wrong, and on a topic you met today you will not catch it. These cover the same ground and were made by people who do this for a living, so they are what you hold the explanation up against. They are other people's work and we only link to them, so judge them for yourself.
4 hand-picked resources
Free · sign inVideos, official docs and articles covering the same ground, each opened and annotated by hand. They are what you check the assistant against on a day you cannot yet catch it being wrong.
Build it
40 minDeliberately cause five different exceptions: NameError, TypeError, KeyError, IndexError and ValueError. For each, copy the stack trace into a file and write one sentence naming the failing line and the cause. Then take one of them, catch it specifically, and decide honestly whether catching it improved anything.
Recall it
20 minAnswer out loud, reveal, then mark honestly whether you had it. That score is the only thing on this page you do not get to choose.
4 recall questions
Free · sign inQuestions you answer from memory, then grade yourself against the real answer. The score is carried into the mastery rating below it, so an honest miss cannot quietly become a tick.
Rate it
Completion and mastery are tracked separately. Be honest, because an inflated rating only means the concept resurfaces sooner.
Mastery tracking
Free · sign inRate yourself against five named criteria per concept. Completion and mastery are tracked separately, and anything you rate shakily comes back automatically on a spaced schedule.
Recap
- 01An exception travels up the call stack until something catches it
- 02The bottom of a trace is where it broke; your lowest own line is usually the clue
- 03Catch specific exceptions, and only when you can do something useful
- 04Failing loudly at the cause beats failing quietly somewhere else
Your progress
Free · sign inMark days complete, pick up where you left off across devices, and watch completion and mastery diverge. Free, and the account exists only so ninety days of work cannot vanish with a cleared browser.