MutaFix run: more-itertools-004

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

fixedoutcome
52swall time
3model calls
$0.0042API cost
Benchmark ground truth (hidden from the agent)
more_itertools/recipes.py:801 · operator BINOP · function more_itertools/recipes.py::_sliding_window_deque
- window = deque(islice(iterator, (n + 1)), maxlen=n)   (injected bug)+ window = deque(islice(iterator, n - 1), maxlen=n)   (original)
retriever rank 1 of 20 · ranker position 1 · patched the right function yes · exact restore no

Trace

reproduce
+12.23s
1 failing test(s) · 1 failed, 767 passed · 12.23s
failing tests and errors
tests/test_recipes.py::SlidingWindowTests::test_deque_version
tests/test_recipes.py::SlidingWindowTests::test_deque_version
E   AssertionError: Tuples differ: ('2', '3', '4', '5', '6', '7', '8', '9', '1[514 chars]'96') != ('0', '1', '2', '3', '4', '5', '6', '7', '8[512 chars]'94')
E   
E   First differing element 0:
E   '2'
E   '0'
E   
E   Diff is 914 characters long. Set self.maxDiff to None to see it.
trace
+19.21s
re-ran 1 test file(s) with the trace plugin: 1 failing and 147 passing tests, 2 library functions ran in a failing test · 6.93s
tests/test_recipes.py
retrieve
+19.21s
280 functions indexed, 4 reachable from tests/test_recipes.py::SlidingWindowTests::test_deque_version in the static call graph. Kept 20 candidates, ranked by spectrum score (Ochiai), call graph and BM25 break ties.
candidates in retriever order
  1. more_itertools/recipes.py::_sliding_window_deque call depth 2 · Ochiai 1.00 (failing 1, passing 0)
  2. more_itertools/recipes.py::sliding_window call depth 1 · Ochiai 0.58 (failing 1, passing 2)
  3. more_itertools/recipes.py::_sliding_window_islice call depth 2 · Ochiai 0.00 (failing 0, passing 1)
  4. more_itertools/recipes.py::pairwise call depth 2 · Ochiai 0.00 (failing 0, passing 2)
  5. more_itertools/more.py::windowed call depth - · Ochiai 0.00 (failing 0, passing 0)
  6. more_itertools/recipes.py::all_equal call depth - · Ochiai 0.00 (failing 0, passing 7)
  7. more_itertools/more.py::all_unique call depth - · Ochiai 0.00 (failing 0, passing 0)
  8. more_itertools/recipes.py::running_max call depth - · Ochiai 0.00 (failing 0, passing 3)
  9. more_itertools/more.py::is_sorted call depth - · Ochiai 0.00 (failing 0, passing 0)
  10. more_itertools/recipes.py::running_median call depth - · Ochiai 0.00 (failing 0, passing 4)
  11. more_itertools/more.py::replace call depth - · Ochiai 0.00 (failing 0, passing 0)
  12. more_itertools/more.py::gray_product call depth - · Ochiai 0.00 (failing 0, passing 0)
  13. more_itertools/more.py::substrings call depth - · Ochiai 0.00 (failing 0, passing 0)
  14. more_itertools/recipes.py::running_statistics call depth - · Ochiai 0.00 (failing 0, passing 3)
  15. more_itertools/more.py::make_decorator call depth - · Ochiai 0.00 (failing 0, passing 0)
  16. more_itertools/recipes.py::unique_everseen call depth - · Ochiai 0.00 (failing 0, passing 5)
  17. more_itertools/more.py::stagger call depth - · Ochiai 0.00 (failing 0, passing 0)
  18. more_itertools/more.py::adjacent call depth - · Ochiai 0.00 (failing 0, passing 0)
  19. more_itertools/more.py::classify_unique call depth - · Ochiai 0.00 (failing 0, passing 0)
  20. more_itertools/more.py::zip_broadcast call depth - · Ochiai 0.00 (failing 0, passing 0)
rank
+19.21s
spectrum order kept (no model call)
  1. more_itertools/recipes.py::_sliding_window_deque
  2. more_itertools/recipes.py::sliding_window
  3. more_itertools/recipes.py::_sliding_window_islice
  4. more_itertools/recipes.py::pairwise
  5. more_itertools/more.py::windowed
read
+21.27s
turn 1 · NVIDIA-Nemotron-3-Nano-30B-A3B · 2777 in / 109 out · 2.06s · $0.00019

read more_itertools/recipes.py::_sliding_window_deque

The failing test expects the first window to start with '0', but the current implementation yields '2' as the first element. This suggests an off-by-one error in the deque initialization or iteration logic. The _sliding_window_deque function is the most likely culprit since it directly handles the sliding window with a fixed-size deque and is the only function called for large n (n=95 in the test).

patch
+24.38s
turn 2 · NVIDIA-Nemotron-3-Nano-30B-A3B · 3038 in / 201 out · 2.78s · $0.00023

The issue is in the initialization of the deque. The current code uses `islice(iterator, (n + 1))` which takes n+1 elements, but the sliding window should start with exactly n elements. This causes the first window to be offset by one element. By changing it to `islice(iterator, n)`, the deque is initialized with exactly n elements, matching the expected behavior of the test.

--- a/more_itertools/recipes.py+++ b/more_itertools/recipes.py@@ -799,5 +799,5 @@     # Normal path for other values of n.     iterator = iter(iterable)-    window = deque(islice(iterator, (n + 1)), maxlen=n)+    window = deque(islice(iterator, n), maxlen=n)     for x in iterator:         window.append(x)

tests: 1 failing (target tests) 1 failed

tests/test_recipes.py::SlidingWindowTests::test_deque_version
patch
+51.53s
turn 3 · nemotron-3-super-120b-a12b · 3433 in / 3058 out · 14.42s · $0.00378

The original implementation incorrectly initialized the deque with n+1 elements and lacked an initial yield, causing the first window to be offset. The fix initializes the deque with exactly n elements, yields the first window if full, then slides the window by appending new elements and yielding thereafter. This matches the expected sliding window behavior.

--- a/more_itertools/recipes.py+++ b/more_itertools/recipes.py@@ -799,5 +799,7 @@     # Normal path for other values of n.     iterator = iter(iterable)-    window = deque(islice(iterator, (n + 1)), maxlen=n)+    window = deque(islice(iterator, n), maxlen=n)+    if len(window) == n:+        yield tuple(window)     for x in iterator:         window.append(x)

tests: all tests pass 768 passed

model reasoning (excerpt)
We need to re-evaluate. The test expects:
all_windows[0] = tuple(map(str, range(95))) -> strings '0' through '94'
all_windows[-1] = tuple(map(str, range(5, 100))) -> strings '5' through '99'

Our current version gave first window starting with '1'. So we are still off by one.

Let's think about what the algorithm does:

Original code:
    iterator = iter(iterable)
    window = deque(islice(iterator, (n + 1)), maxlen=n)
    for x in iterator:
        window.append(x)
        yield tuple(window)

With our changed version:
    window = deque(islice(iterator, n), maxlen=n)
    for x in iterator:
        window.append(x)
        yield tuple(window)

But note: when we create the deque with maxlen=n and initialize it with n elements from islice, the deque already contains those n elements. Then we immediately enter the loop and append the next element from iterator, making the window size n+1? Actually, deque with maxlen=n will drop the oldest when we append beyond its size. Let's simulate:

Suppose n=3, iterable = [0,1,2,3,4,...]

Initialize window with islice(iterator, 3) -> [0,1,2] (deque with maxlen=3, so it holds exactly these three).

Now enter loop: x = next(iterator) = 3.
window.append(3) -> deque becomes [1,2,3] (because maxlen=3, drops leftmost 0).
yield tuple(window) -> (1,2,3)

So first yielded window is [1,2,3], missing 0. That's why we got first window starting with 1.

To get the first window to be [0,1,2], we need to yield the initial window before appending anything

Final patch

--- a/more_itertools/recipes.py+++ b/more_itertools/recipes.py@@ -799,5 +799,7 @@     # Normal path for other values of n.     iterator = iter(iterable)-    window = deque(islice(iterator, (n + 1)), maxlen=n)+    window = deque(islice(iterator, n), maxlen=n)+    if len(window) == n:+        yield tuple(window)     for x in iterator:         window.append(x)