From 1f1374009b681814642ca199136815b223fd90ae Mon Sep 17 00:00:00 2001 From: =?utf8?q?=C5=81ukasz?= Date: Sun, 19 Jul 2026 08:06:09 +0200 Subject: [PATCH] gh-154001: Avoid division by zero in binomialvariate (GH-154004) --- Lib/random.py | 6 +++++- Lib/test/test_random.py | 8 ++++++++ .../2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst | 2 ++ 3 files changed, 15 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst diff --git a/Lib/random.py b/Lib/random.py index 4541267bab86..7db761034509 100644 --- a/Lib/random.py +++ b/Lib/random.py @@ -861,7 +861,11 @@ class Random(_random.Random): u = random() u -= 0.5 us = 0.5 - _fabs(u) - k = _floor((2.0 * a / us + b) * u + c) + try: + k = _floor((2.0 * a / us + b) * u + c) + except ZeroDivisionError: + # Reject case where random() returned 0.0 + continue if k < 0 or k > n: continue v = random() diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py index dbd3b855f536..8d093ab1b701 100644 --- a/Lib/test/test_random.py +++ b/Lib/test/test_random.py @@ -1082,6 +1082,14 @@ class TestDistributions(unittest.TestCase): 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 diff --git a/Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst b/Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst new file mode 100644 index 000000000000..ff019aa36188 --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst @@ -0,0 +1,2 @@ +Fix :func:`random.binomialvariate` raising :exc:`ZeroDivisionError` +when :func:`random.random` returns zero. -- 2.47.3