fix: handle a=0 as valid answer index in build_qa_turn #3488
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Fixes EleutherAI#3452 When answer is an integer index into choices, a=0 should be treated as a valid answer, not as falsy. Previously, the condition 'if a and not gen_prefix' incorrectly treated a=0 as falsy, causing the target_delimiter to be skipped for few-shot examples where the answer was the first choice. This caused inconsistent formatting: - Few-shot examples: 'Answer:A' (no space) - Model predictions: ' A' (with leading space from target_delimiter) The fix explicitly checks 'a is not None and a != ""' instead of relying on truthiness. Added regression tests for answer index 0 and non-zero cases.
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baberabb
approved these changes
Jan 7, 2026
Contributor
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Great catch! This was a sneaky one. Thanks for the fix! |
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Summary
Fixes #3452 - Performance decreasing when passing from 0 to few shots
Root Cause
In
build_qa_turn(), the conditionif a and not gen_prefixincorrectly treateda=0(a valid answer index) as falsy, causing thetarget_delimiterto be skipped for few-shot examples where the answer was the first choice.The Bug
When a few-shot example has
answer=0:Answer:A(no space - wrong)Answer: A(with space - correct)This inconsistency confused models because few-shot examples showed a different format than what the model was asked to predict.
The Fix
Changed truthiness check to explicit None/empty check:
Testing
Added 2 regression tests for answer index 0 and non-zero cases
All 48 fewshot context tests pass