Issue 28475: Improve error message for random.sample() with k < 0. (Contributed by Francisco Couzo).

rhettinger · rhettinger · commit bf87126a636b · 2016-11-21T14:34:33.000-08:00
diff --git a/Lib/random.py b/Lib/random.py
@@ -314,7 +314,7 @@ def sample(self, population, k):
         randbelow = self._randbelow
         n = len(population)
         if not 0 <= k <= n:
-            raise ValueError("Sample larger than population")
+            raise ValueError("Sample larger than population or is negative")
         result = [None] * k
         setsize = 21        # size of a small set minus size of an empty list
         if k > 5:
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
@@ -110,6 +110,7 @@ def test_sample(self):
         self.assertEqual(self.gen.sample([], 0), [])  # test edge case N==k==0
         # Exception raised if size of sample exceeds that of population
         self.assertRaises(ValueError, self.gen.sample, population, N+1)
+        self.assertRaises(ValueError, self.gen.sample, [], -1)
 
     def test_sample_distribution(self):
         # For the entire allowable range of 0 <= k <= N, validate that
