From 30d00e54dde47b11f5b338aaba17760b641e1705 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Sat, 29 Oct 2016 16:55:36 -0700 Subject: Issue #18844: Make the various ways for specifing weights produce the same results. --- Lib/random.py | 7 ++++--- Lib/test/test_random.py | 16 ++++++++++++++++ Misc/NEWS | 3 +++ 3 files changed, 23 insertions(+), 3 deletions(-) diff --git a/Lib/random.py b/Lib/random.py index ef8cb05..a047444 100644 --- a/Lib/random.py +++ b/Lib/random.py @@ -344,10 +344,12 @@ class Random(_random.Random): the selections are made with equal probability. """ + random = self.random if cum_weights is None: if weights is None: - choice = self.choice - return [choice(population) for i in range(k)] + _int = int + total = len(population) + return [population[_int(random() * total)] for i in range(k)] else: cum_weights = list(_itertools.accumulate(weights)) elif weights is not None: @@ -355,7 +357,6 @@ class Random(_random.Random): if len(cum_weights) != len(population): raise ValueError('The number of weights does not match the population') bisect = _bisect.bisect - random = self.random total = cum_weights[-1] return [population[bisect(cum_weights, random() * total)] for i in range(k)] diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py index 4d5a874..dd27152 100644 --- a/Lib/test/test_random.py +++ b/Lib/test/test_random.py @@ -629,6 +629,22 @@ class MersenneTwister_TestBasicOps(TestBasicOps, unittest.TestCase): self.assertTrue(stop < x <= start) 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): # Reflection to right half of complex plane if z < 0.5: diff --git a/Misc/NEWS b/Misc/NEWS index 75f0ba6..d49162b 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -34,6 +34,9 @@ Library - Issue #27275: Fixed implementation of pop() and popitem() methods in subclasses of accelerated OrderedDict. +- Issue #18844: The various ways of specifing weights for random.choices() + now produce the same result sequences. + - Issue #28255: calendar.TextCalendar().prmonth() no longer prints a space at the start of new line after printing a month's calendar. Patch by Xiang Zhang. -- cgit v0.12