[Python-Dev] a note in random.shuffle.__doc__ ...
aleaxit at gmail.com
Sat Jun 10 21:04:23 CEST 2006
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
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!
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