mean and median crash on an empty list

Done

/home/devdi/devswarm/evals/tasks/empty_input_statistics/repo · 2026-11-09 16:14:28 UTC · took 26.6s

Plan (done)
Code (done)
Test (done)
Review (done)
Finish (done)

Cost

$0.0028

Tests

Passed

Iterations

Re-plans

LLM calls

Prompt read from cache

79%

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Agent	Cost	Cache read	Cache write	Input	Output
planner	$0.0006	5,625	843	8	846
coder	$0.0007	8,567	1,863	8	843
tester	$0.0010	9,644	2,544	8	1,233
reviewer	$0.0004	1,727	1,702	4	396

Timeline

planner iteration 1 Finished 3 calls · 7,322 tokens · $0.0006 · 6.0s

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coder iteration 1 Finished 3 calls · 11.3K tokens · $0.0007 · 5.3s

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tester iteration 1 Finished 3 calls · 13.4K tokens · $0.0010 · 10.6s

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verify iteration 1 Passed 0.6s

.......                                                                  [100%]
7 passed in 0.02s

reviewer iteration 1 Finished 1 calls · 3,829 tokens · $0.0004 · 3.5s

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Final diff

diff --git a/stats.py b/stats.py
index 1367357..0aa8739 100644
--- a/stats.py
+++ b/stats.py
@@ -1,8 +1,12 @@
 def mean(values: list[float]) -> float:
+    if not values:
+        return 0.0
     return sum(values) / len(values)
 
 
 def median(values: list[float]) -> float:
+    if not values:
+        return 0.0
     ordered = sorted(values)
     middle = len(ordered) // 2
     if len(ordered) % 2:
diff --git a/test_stats.py b/test_stats.py
index 7b17903..b953ae2 100644
--- a/test_stats.py
+++ b/test_stats.py
@@ -3,8 +3,40 @@ from stats import mean, median
 
 def test_mean():
     assert mean([1, 2, 3]) == 2
+    assert mean([]) == 0.0
 
 
 def test_median():
     assert median([3, 1, 2]) == 2
     assert median([1, 2, 3, 4]) == 2.5
+    assert median([]) == 0.0
+
+
+def test_mean_empty_returns_float():
+    result = mean([])
+    assert isinstance(result, float)
+    assert result == 0.0
+
+
+def test_median_empty_returns_float():
+    result = median([])
+    assert isinstance(result, float)
+    assert result == 0.0
+
+
+def test_mean_single_and_negative_values_unchanged():
+    assert mean([5]) == 5
+    assert mean([-1, 1]) == 0
+    assert mean([1.5, 2.5]) == 2.0
+
+
+def test_median_single_and_unsorted_unchanged():
+    assert median([7]) == 7
+    assert median([4, -2, 10, 0, 3]) == 3
+    assert median([10, 2, 8, 4]) == 6
+
+
+def test_median_does_not_mutate_input():
+    values = [3, 1, 2]
+    median(values)
+    assert values == [3, 1, 2]