When something goes wrong, Python stops and prints a traceback. It looks intimidating and is actually a gift: the exact line and a one-line description of the problem.

Read it bottom up

The final line is ErrorType: message — that is what happened. The lines above show how the program reached that point, most recent call last. In a short script there is one frame, so the last two lines are all you need.

Error	Means	Usual cause
`SyntaxError`	Could not parse the line	Missing colon, bracket or quote
`IndentationError`	Spacing is wrong	Body of a block not indented
`NameError`	Unknown name	Typo, or used before created
`TypeError`	Wrong kind of value	Adding a string to a number
`ValueError`	Right type, impossible value	`int("abc")`
`IndexError`	Position does not exist	Off-by-one on a list
`KeyError`	Key not in the dictionary	Reading before writing

The caret line

From Python 3.11 onward the traceback underlines the exact sub-expression that failed, not just the line. On total / count the carets sit under total / count itself, which is invaluable when one line contains several operations. Older versions show the line only.

Syntax errors point at the line after

A missing closing bracket is often reported on the next line, because Python only notices when it reaches something unexpected. If the reported line looks fine, check the one above it.