python random.shuffle's randomness

问题

Following is from python website, about

random.shuffle(x[, random])

Shuffle the sequence x in place. The optional argument random is a 0-argument function returning a random float in [0.0, 1.0); by default, this is the function random().

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.

If I want to repeat getting a random permutation of ['a'..'k'], it seems shuffle will NOT give me the randomness. Is my understanding right?

Thank you!

回答1:

You don't have anything to worry about. While under len(x) is under 2000, random.shuffle should work just fine.

回答2:

For a sequence of length 11, there are 11! or 39,916,800 (~ 2^25.3) possible permutations. For the Mersienne Twister (Python's random algorithm) the period is 2¹⁹⁹³⁷ − 1. In other words, you'll be fine.

来源：https://stackoverflow.com/questions/3160214/python-random-shuffles-randomness