[Python-Dev] a note in random.shuffle.__doc__ ...
Alex Martelli
aleaxit at gmail.com
Sat Jun 10 21:04:23 CEST 2006
...claims:
Note that for even rather small len(x), the total number of
permutations of x is larger than the period of most random number
generators; this implies that "most" permutations of a long
sequence can never be generated.
Now -- why would the behavior of "most" random number generators be
relevant here? The module's docs claim, for its specific Mersenne
Twister generator, a period of 2**19997-1, which is (e.g.) a
comfortable
130128673800676351960752618754658780303412233749552410245124492452914636
028095467780746435724876612802011164778042889281426609505759158196749438
742986040468247017174321241233929215223326801091468184945617565998894057
859403269022650639413550466514556014961826309062543 times larger than
the number of permutations of 2000 items, which doesn't really feel
to me like a "rather small len(x)" in this context (what I'm most
often shuffling is just a pack of cards -- len(x)==52 -- for example).
I suspect that the note is just a fossil from a time when the default
random number generator was Whichman-Hill, with a much shorter
period. Should this note just be removed, or instead somehow
reworded to point out that this is not in fact a problem for the
module's current default random number generator? Opinions welcome!
Alex
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