Exceptions

Handle errors deliberately instead of crashing.

Loading your progress…Next: 5.5 Debugging

In this lesson8 parts

01One bad row
02Reading a traceback
03try and except
04Asking until it is valid
05Several excepts, else and finally
06Raising your own
07Where exceptions mislead
08Recap, your challenge, and next

Key terms

The words this lesson introduces, each in one line. The module’s glossary collects them all.

exception: An object Python raises when a line can not be carried out; unhandled, it stops the program.
handle: Catch an exception with except, so the program carries on.
raise: Create an exception and stop the function with it: raise ValueError(...).
traceback: The report Python prints for an unhandled exception: the calls that led to it, and the error itself on the last line.

Quiz 5 questions

Your first pick on each question is the one that counts, and a right one earns a coin. Getting one wrong here is how the lesson sticks.

Practice

Problems to solve in your own notebook. Each states the problem, not the steps: working out the steps is the exercise. Level A applies the lesson, B combines it with earlier ones, C stretches it.

The self-checking notebook for this lesson is Notebook 2 · Files and Exceptions.

Common mistakes

What you will see when it goes wrong, why it happens, and the fix.

Where it’s used

Where this lesson’s ideas turn up in real work.