Time: 0:00
Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).
This bug belongs to the type errors pattern
Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.
What went wrong: Built-in sum() initializes its accumulator to integer 0. Adding a string to 0 raises a TypeError.
The fix: Use str.join() to concatenate strings: ''.join(words)
Remember: In Python, sum() cannot concatenate strings; use ''.join(strings).
The pattern behind it: type errors.
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