try/except — the patterns AI misuses (step 8/8) · read the failure

Checkpoint

One last thing before we move on. Same surface as a write step — but the lesson doesn't complete until this passes.

Last drill. Cursor wrote summarize_order to look up an item's price, multiply it by a quantity it parses from a string, and return a total. Three failure modes:

prices[item] raises KeyError if the item isn't in the catalog.
int(qty_text) raises ValueError if the string isn't a number.
everything else (a real bug you didn't anticipate) should crash.

The starter has a single except Exception: that swallows all three. The last order in the list is a real bug — the caller passed a list instead of an item name, which raises TypeError. The test harness at the bottom catches that and prints bug: crashed loudly so you can see the bug escaping. Right now it prints invalid instead — the broad except is hiding it.

Fix the except: catch KeyError and ValueError together with a tuple, return "invalid" for either case, and let any other exception fly through.

Expected output:

20
invalid
invalid
bug: crashed loudly

Checkpoint

One last thing before we move on. Same surface as a write step — but the lesson doesn't complete until this passes.

Last drill. Cursor wrote summarize_order to look up an item's price, multiply it by a quantity it parses from a string, and return a total. Three failure modes:

prices[item] raises KeyError if the item isn't in the catalog.
int(qty_text) raises ValueError if the string isn't a number.
everything else (a real bug you didn't anticipate) should crash.

Fix the except: catch KeyError and ValueError together with a tuple, return "invalid" for either case, and let any other exception fly through.

Expected output:

20
invalid
invalid
bug: crashed loudly

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try/except — the patterns AI misuses — step 8 of 8