[Python-Dev] a note in random.shuffle.doc ... (original) (raw)

Josiah Carlson jcarlson at uci.edu
Sat Jun 10 21:52:05 CEST 2006

Alex Martelli <aleaxit at gmail.com> wrote:

...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. [snip] 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!

I'm recovering from a migraine, but here are my thoughts on the topic...

The number of permutations of n items is n!, which is > (n/2)^(n/2). Solve: 219997 < (n/2)^(n/2) log_2(219997) < log_2((n/2)^(n/2)) 19997 < (n/2)*log(n/2)

Certainly with n >= 4096, the above holds (2048 * 11 = 22528)

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