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Raymond Hettinger 2016-10-29 16:57:09 -07:00
commit ba25f61490
2 changed files with 20 additions and 3 deletions
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7
Lib/random.py
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@ -344,10 +344,12 @@ class Random(_random.Random):
the selections are made with equal probability. the selections are made with equal probability.
""" """
random = self.random
if cum_weights is None: if cum_weights is None:
if weights is None: if weights is None:
choice = self.choice _int = int
return [choice(population) for i in range(k)] total = len(population)
return [population[_int(random() * total)] for i in range(k)]
else: else:
cum_weights = list(_itertools.accumulate(weights)) cum_weights = list(_itertools.accumulate(weights))
elif weights is not None: elif weights is not None:
@ -355,7 +357,6 @@ class Random(_random.Random):
if len(cum_weights) != len(population): if len(cum_weights) != len(population):
raise ValueError('The number of weights does not match the population') raise ValueError('The number of weights does not match the population')
bisect = _bisect.bisect bisect = _bisect.bisect
random = self.random
total = cum_weights[-1] total = cum_weights[-1]
return [population[bisect(cum_weights, random() * total)] for i in range(k)] return [population[bisect(cum_weights, random() * total)] for i in range(k)]

16
Lib/test/test_random.py
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@ -625,6 +625,22 @@ class MersenneTwister_TestBasicOps(TestBasicOps, unittest.TestCase):
self.assertTrue(stop < x <= start) self.assertTrue(stop < x <= start)
self.assertEqual((x+stop)%step, 0) self.assertEqual((x+stop)%step, 0)
def test_choices_algorithms(self):
# The various ways of specifing weights should produce the same results
choices = self.gen.choices
n = 13132817
self.gen.seed(8675309)
a = self.gen.choices(range(n), k=10000)
self.gen.seed(8675309)
b = self.gen.choices(range(n), [1]*n, k=10000)
self.assertEqual(a, b)
self.gen.seed(8675309)
c = self.gen.choices(range(n), cum_weights=range(1, n+1), k=10000)
self.assertEqual(a, c)
def gamma(z, sqrt2pi=(2.0*pi)**0.5): def gamma(z, sqrt2pi=(2.0*pi)**0.5):
# Reflection to right half of complex plane # Reflection to right half of complex plane
if z < 0.5: if z < 0.5: