New submission from David Benbennick: Since Python 2.1 [1], when random.shuffle was added, the documentation has said:
"""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.""" This comment is incorrect and misleading. In fact, I claim that shuffle can produce "all" permutations for any representable sequence. To shuffle a sequence of length N requires log(N!) ~ N * log(N/e) bits of randomness [2]. The random module provides a generator with "a period of 2**19937-1", meaning you can get 2**19937 bits of randomness out of it before it starts repeating. All of which is to say that any representable sequence, say N < 2**50, will need no more than 2**60 bits of randomness to shuffle. That is well within the period of the random number generator. Attached is a patch that deletes the comment. An illustration of this misconception is at [3]. 1: http://docs.python.org/release/2.1/lib/module-random.html 2: https://en.wikipedia.org/wiki/Factorial#Rate_of_growth_and_approximations_for_large_n 3: http://stackoverflow.com/questions/3062741/maximal-length-of-list-to-shuffle-with-python-random-shuffle ---------- assignee: docs@python components: Documentation files: mywork.patch keywords: patch messages: 196971 nosy: dbenbenn, docs@python priority: normal severity: normal status: open title: Remove misleading documentation for random.shuffle Added file: http://bugs.python.org/file31593/mywork.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue18928> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
