From 7fc633f5a56d9e672cd24133e2e1376347abac6c Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <rhettinger@users.noreply.github.com>
Date: Tue, 4 Dec 2018 00:13:38 -0800
Subject: [PATCH] Add comments regarding speed/space/entropy trade-offs
(GH-10885)
---
Lib/random.py | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/Lib/random.py b/Lib/random.py
index 4b51b6696b..a7a86070c0 100644
--- a/Lib/random.py
+++ b/Lib/random.py
@@ -333,6 +333,19 @@ class Random(_random.Random):
# preferred since the list takes less space than the
# set and it doesn't suffer from frequent reselections.
+ # The number of calls to _randbelow() is kept at or near k, the
+ # theoretical minimum. This is important because running time
+ # is dominated by _randbelow() and because it extracts the
+ # least entropy from the underlying random number generators.
+
+ # Memory requirements are kept to the smaller of a k-length
+ # set or an n-length list.
+
+ # There are other sampling algorithms that do not require
+ # auxiliary memory, but they were rejected because they made
+ # too many calls to _randbelow(), making them slower and
+ # causing them to eat more entropy than necessary.
+
if isinstance(population, _Set):
population = tuple(population)
if not isinstance(population, _Sequence):
--
2.18.1