On Mon, Dec 26, 2011 at 2:00 PM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > The implementation of getrandbits is not documented at all. You would > have to read the C source of the _random module to find out how the > default pseudo-random number generator produces random bits. But note the > leading underscore: _random is a private implementation detail. > > However the existence and use of random.Random.getrandbits is public, > documented, and guaranteed.
It's that last line where I find disagreement between documentation and source code. """Class Random can also be subclassed if you want to use a different basic generator of your own devising: in that case, override the random(), seed(), getstate(), and setstate() methods. Optionally, a new generator can supply a getrandbits() method — this allows randrange() to produce selections over an arbitrarily large range.""" My reading of this is that, if I were to write my own generator, I could provide that method and gain perfection. It's not until you dig somewhat that you find out that the default generator actually does provide getrandbits, meaning that the default randrange can actually be used for arbitrarily large ranges. Yes, it IS documented, but in separate places and somewhat as an afterthought; in the 2.x documentation it's shown as "new in 2.4", which explains this. Unfortunately my brain isn't really running on all cylinders at the moment and I can't come up with a better wording, but is there some way this could be stated up in the same top paragraph that explains about 53-bit precision and 2**19937-1 period? That's where I got my original information from; I didn't go down to the individual function definitions, which is the only place that it's stated that the Mersenne Twister does include getrandbits (and which assumes that you've read the top section that states that Mersenne Twister is the default implementation). ChrisA -- http://mail.python.org/mailman/listinfo/python-list
