Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the logic errors pattern
The wrong operator, an inverted condition, a formula the right way round but backwards.
What went wrong: The is operator compares memory addresses (object identity), not mathematical values. CPython caches small integers from -5 to 256, but larger numbers are separate objects.
The fix: Use the equality operator (==) to compare values: return account_id == target_id
Remember: In Python, use == for value equality; only use is for singleton checks like is None.
The pattern behind it: logic errors.
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