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Add comments regarding speed/space/entropy trade-offs (GH-10885)

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Raymond Hettinger 2018-12-04 00:13:38 -08:00 committed by Miss Islington (bot)
parent 1747334794
commit 7fc633f5a5
1 changed files with 13 additions and 0 deletions
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13
Lib/random.py
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@ -333,6 +333,19 @@ class Random(_random.Random):
# preferred since the list takes less space than the # preferred since the list takes less space than the
# set and it doesn't suffer from frequent reselections. # 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): if isinstance(population, _Set):
population = tuple(population) population = tuple(population)
if not isinstance(population, _Sequence): if not isinstance(population, _Sequence):