MutaFix run: boltons-011

ranker nvidia/NVIDIA-Nemotron-3-Nano-30B-A3B · patcher nvidia/nemotron-3-super-120b-a12b · via Nebius Token Factory

fixedoutcome
42swall time
3model calls
$0.0046API cost
Benchmark ground truth (hidden from the agent)
boltons/listutils.py:185 · operator BINOP · function boltons/listutils.py::BarrelList.iter_slice
- return islice(reversed(self), (length - 1 + start), length - 1 - stop, -step)   (injected bug)+ return islice(reversed(self), length - 1 - start, length - 1 - stop, -step)   (original)
retriever rank 2 of 20 · ranker position 2 · patched the right function yes · exact restore yes

Trace

reproduce
+2.92s
2 failing test(s) · 2 failed, 523 passed · 2.92s
failing tests and errors
tests/test_listutils.py::test_barrel_list
tests/test_listutils.py::test_barrellist_slicing_matches_list
tests/test_listutils.py::test_barrel_list
E   assert [] == [50508, 46607, 46428, 43442]
E     
E     Right contains 4 more items, first extra item: 50508
E     Use -v to get more diff
tests/test_listutils.py::test_barrellist_slicing_matches_list
E   ValueError: Indices for islice() must be None or an integer: 0 <= x <= sys.maxsize.
trace
+3.38s
re-ran 1 test file(s) with the trace plugin: 2 failing and 9 passing tests, 15 library functions ran in a failing test · 0.33s
tests/test_listutils.py
retrieve
+3.38s
923 functions indexed, 121 reachable from tests/test_listutils.py::test_barrel_list in the static call graph. Kept 20 candidates, ranked by spectrum score (Ochiai), call graph and BM25 break ties.
candidates in retriever order
  1. boltons/listutils.py::BarrelList.__reversed__ call depth 1 · Ochiai 1.00 (failing 2, passing 0)
  2. boltons/listutils.py::BarrelList.iter_slice call depth 2 · Ochiai 1.00 (failing 2, passing 0)
  3. boltons/listutils.py::BarrelList.from_iterable call depth 2 · Ochiai 1.00 (failing 2, passing 0)
  4. boltons/listutils.py::BarrelList.__repr__ call depth 1 · Ochiai 0.71 (failing 1, passing 0)
  5. boltons/listutils.py::BarrelList.sort call depth 1 · Ochiai 0.50 (failing 1, passing 1)
  6. boltons/listutils.py::BarrelList.__getitem__ call depth 1 · Ochiai 0.50 (failing 2, passing 6)
  7. boltons/listutils.py::BarrelList.__iter__ call depth 1 · Ochiai 0.50 (failing 2, passing 6)
  8. boltons/listutils.py::BarrelList.extend call depth 1 · Ochiai 0.47 (failing 2, passing 7)
  9. boltons/listutils.py::BarrelList.__init__ call depth 1 · Ochiai 0.45 (failing 2, passing 8)
  10. boltons/listutils.py::BarrelList.__len__ call depth 1 · Ochiai 0.45 (failing 2, passing 8)
  11. boltons/listutils.py::BarrelList.insert call depth 1 · Ochiai 0.27 (failing 1, passing 6)
  12. boltons/listutils.py::BarrelList.pop call depth 1 · Ochiai 0.27 (failing 1, passing 6)
  13. boltons/listutils.py::BarrelList._balance_list call depth 1 · Ochiai 0.25 (failing 1, passing 7)
  14. boltons/listutils.py::BarrelList._cur_size_limit call depth 2 · Ochiai 0.25 (failing 1, passing 7)
  15. boltons/listutils.py::BarrelList._translate_index call depth 2 · Ochiai 0.24 (failing 1, passing 8)
  16. boltons/setutils.py::IndexedSet.sort call depth 1 · Ochiai 0.00 (failing 0, passing 0)
  17. boltons/setutils.py::IndexedSet.pop call depth 1 · Ochiai 0.00 (failing 0, passing 0)
  18. boltons/dictutils.py::OrderedMultiDict.sorted call depth 1 · Ochiai 0.00 (failing 0, passing 0)
  19. boltons/urlutils.py::OrderedMultiDict.sorted call depth 1 · Ochiai 0.00 (failing 0, passing 0)
  20. boltons/listutils.py::BarrelList.__setitem__ call depth 1 · Ochiai 0.00 (failing 0, passing 0)
rank
+3.38s
spectrum order kept (no model call)
  1. boltons/listutils.py::BarrelList.__reversed__
  2. boltons/listutils.py::BarrelList.iter_slice
  3. boltons/listutils.py::BarrelList.from_iterable
  4. boltons/listutils.py::BarrelList.__repr__
  5. boltons/listutils.py::BarrelList.sort
read
+4.73s
turn 1 · NVIDIA-Nemotron-3-Nano-30B-A3B · 2008 in / 82 out · 1.34s · $0.00014

read boltons/listutils.py::BarrelList.iter_slice

The failing test test_barrellist_slicing_matches_list raises ValueError: Indices for islice() must be None or an integer, which suggests an issue in iter_slice where slice indices are computed incorrectly, likely due to negative step handling or incorrect calculation of start/stop positions.

patch
+6.82s
turn 2 · NVIDIA-Nemotron-3-Nano-30B-A3B · 2251 in / 202 out · 1.79s · $0.00018

The issue is in the handling of negative step in iter_slice. When step is negative, the code incorrectly uses `-step` as the step size for islice, which turns a negative step into a positive one, causing the ValueError. The correct approach is to pass the original `step` (which is negative) directly to islice, as it expects the actual step value, including its sign. The indices calculation for start and stop also needs adjustment when step is negative to maintain correct slicing semantics.

--- a/boltons/listutils.py+++ b/boltons/listutils.py@@ -183,5 +183,5 @@         start, stop, step = slice(start, stop, step).indices(length)         if step < 0:-            return islice(reversed(self), (length - 1 + start), length - 1 - stop, -step)+            return islice(reversed(self), (length - 1 + start), length - 1 - stop, step)         return islice(self, start, stop, step)

tests: 2 failing (target tests) 2 failed

tests/test_listutils.py::test_barrel_list
tests/test_listutils.py::test_barrellist_slicing_matches_list
patch
+41.75s
turn 3 · nemotron-3-super-120b-a12b · 2579 in / 3869 out · 31.24s · $0.00426

The original code incorrectly added start instead of subtracting it when computing the start index for the reversed iteration. For a negative step slice, the correct mapping to the reversed sequence is to start at index (length-1-start) and stop at (length-1-stop) with a positive step of -step. This fix ensures that islice receives non-negative integer indices and a positive step, resolving the ValueError about indices and step.

--- a/boltons/listutils.py+++ b/boltons/listutils.py@@ -183,5 +183,5 @@         start, stop, step = slice(start, stop, step).indices(length)         if step < 0:-            return islice(reversed(self), (length - 1 + start), length - 1 - stop, -step)+            return islice(reversed(self), (length - 1 - start), length - 1 - stop, -step)         return islice(self, start, stop, step)

tests: all tests pass 525 passed

model reasoning (excerpt)
We need to analyze the error messages:

First test: `ValueError: Step for islice() must be a positive integer or None.` This occurs in test_barrel_list? Actually the traceback might be from the other test? Let's examine both errors.

After our patch, we got two errors:

1. For test_barrel_list: `ValueError: Step for islice() must be a positive integer or None.`

2. For test_barrellist_slicing_matches_list: `ValueError: Indices for islice() must be None or an integer: 0 <= x <= sys.maxsize.`

Our patch changed the step argument from `-step` to `step`. But now we get an error that step must be positive. That means when step is negative, we are passing a negative step to islice, but islice requires step to be positive? Actually, islice does allow negative step? Let's recall: itertools.islice(iterable, start, stop, step) requires step to be a positive integer. Indeed, the documentation says: "If step is supplied and is negative, then the iterable is traversed in reverse order." Wait, I think islice does support negative step? Actually, checking memory: In Python, islice does not support negative step; it raises ValueError: Step for islice() must be a positive integer or None. Yes, that's correct. So islice only accepts non-negative step (positive or None). Therefore, to iterate backwards, we need to reverse the iterable and use positive step.

Thus the original code attempted to do that: they used `islice(reversed(self), ... , -step)` where -step would be positive when step is ne

Final patch

--- a/boltons/listutils.py+++ b/boltons/listutils.py@@ -183,5 +183,5 @@         start, stop, step = slice(start, stop, step).indices(length)         if step < 0:-            return islice(reversed(self), (length - 1 + start), length - 1 - stop, -step)+            return islice(reversed(self), (length - 1 - start), length - 1 - stop, -step)         return islice(self, start, stop, step)