https://github.com/python/cpython/commit/1f1374009b681814642ca199136815b223fd90ae
commit: 1f1374009b681814642ca199136815b223fd90ae
branch: main
author: Łukasz <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-07-19T09:06:09+03:00
summary:
gh-154001: Avoid division by zero in binomialvariate (GH-154004)
files:
A Misc/NEWS.d/next/Library/2026-07-18-17-09-49.gh-issue-154001.3brrUv.rst
M Lib/random.py
M Lib/test/test_random.py
diff --git a/Lib/random.py b/Lib/random.py
index 4541267bab866a..7db761034509d3 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -861,7 +861,11 @@ def binomialvariate(self, n=1, p=0.5):
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 dbd3b855f536a0..8d093ab1b7014a 100644
--- a/Lib/test/test_random.py
+++ b/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
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 00000000000000..ff019aa3618847
--- /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.
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