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gh-135647: fix random.vonmisesvariate() and random.lognormvariate() accept invalid parameters #135717

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gh-135647: fix random.vonmisesvariate() and random.lognormvariate() accept invalid parameters #135717

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gh-135647: fix random.vonmisesvariate() and random.lognormvariate() a…
michaelzheng67 Jun 19, 2025
42abd61
Merge branch 'main' into fix-issue-135647
tim-one Jun 21, 2025
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9 changes: 8 additions & 1 deletion Lib/random.py
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Original file line number Diff line number Diff line change
Expand Up @@ -536,6 +536,8 @@ def triangular(self, low=0.0, high=1.0, mode=None):
def normalvariate(self, mu=0.0, sigma=1.0):
"""Normal distribution.

Conditions on the parameters are sigma > 0.

mu is the mean, and sigma is the standard deviation.

"""
Expand All @@ -544,6 +546,9 @@ def normalvariate(self, mu=0.0, sigma=1.0):
# variables using the ratio of uniform deviates", ACM Trans
# Math Software, 3, (1977), pp257-260.

if sigma <= 0:
raise ValueError("normalvariate: sigma must be > 0.0")

random = self.random
while True:
u1 = random()
Expand Down Expand Up @@ -640,7 +645,9 @@ def vonmisesvariate(self, mu, kappa):

random = self.random
if kappa <= 1e-6:
return TWOPI * random()
if kappa >= 0:
return TWOPI * random()
raise ValueError("vonmisesvariate: kappa must be >= 0.0")

s = 0.5 / kappa
r = s + _sqrt(1.0 + s * s)
Expand Down
9 changes: 6 additions & 3 deletions Lib/test/test_random.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1084,9 +1084,6 @@ def test_constant(self):
(g.expovariate, (float('inf'),), 0.0),
(g.vonmisesvariate, (3.0, float('inf')), 3.0),
(g.gauss, (10.0, 0.0), 10.0),
(g.lognormvariate, (0.0, 0.0), 1.0),
(g.lognormvariate, (-float('inf'), 0.0), 0.0),
(g.normalvariate, (10.0, 0.0), 10.0),
(g.binomialvariate, (0, 0.5), 0),
(g.binomialvariate, (10, 0.0), 0),
(g.binomialvariate, (10, 1.0), 10),
Expand Down Expand Up @@ -1152,7 +1149,13 @@ def test_binomialvariate(self):
# Demonstrate the BTRS works for huge values of n
self.assertTrue(19_000_000 <= B(100_000_000, 0.2) <= 21_000_000)
self.assertTrue(89_000_000 <= B(100_000_000, 0.9) <= 91_000_000)
def test_log_norm_errors(self):
# sigma must be > 0.0
self.assertRaises(ValueError, random.lognormvariate, 1, -2)

def test_von_mises_errors(self):
# kappa must be >= 0.0
self.assertRaises(ValueError, random.vonmisesvariate, 1, -2)

def test_von_mises_range(self):
# Issue 17149: von mises variates were not consistently in the
Expand Down
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