gh-154001: Avoid division by zero in binomialvariate

Author: lkk7

Lib/random.py

@@ -861,6 +861,8 @@ def binomialvariate(self, n=1, p=0.5):
             u = random()
             u -= 0.5
             us = 0.5 - _fabs(u)
+            if us == 0.0:
+                continue
             k = _floor((2.0 * a / us + b) * u + c)
             if k < 0 or k > n:
                 continue

Lib/test/test_random.py

@@ -1082,6 +1082,14 @@ def test_binomialvariate_log_zero(self):
             self.assertIsInstance(result, int)
             self.assertIn(result, range(11))
 
+    def test_binomialvariate_btrs_random_zero(self):
+        for p, expected in ((0.25, 25), (0.75, 75)):
+            with self.subTest(p=p):
+                g = random.Random()
+                with unittest.mock.patch.object(
+                        g, 'random', side_effect=(0.0, 0.5, 0.5)):
+                    self.assertEqual(g.binomialvariate(100, p), expected)
+
     def test_constant(self):
         g = random.Random()
         N = 100

Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst

@@ -0,0 +1,2 @@
+Fix :meth:`random.Random.binomialvariate` raising :exc:`ZeroDivisionError`
+when a random draw is zero.