[Python-checkins] cpython (3.6): Issue #18844: Make the various ways for specifing weights produce the same

Sat Oct 29 19:57:15 EDT 2016

https://hg.python.org/cpython/rev/32bfc81111b6
changeset: 104806:32bfc81111b6
branch: 3.6
parent: 104804:2c2fec17247d
user: Raymond Hettinger <python at rcn.com>
date: Sat Oct 29 16:55:36 2016 -0700
summary:
 Issue #18844: Make the various ways for specifing weights produce the same results.
files:
 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
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -344,10 +344,12 @@
 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 @@
 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
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -629,6 +629,22 @@
 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
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -34,6 +34,9 @@
 - 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.
-- 
Repository URL: https://hg.python.org/cpython
