At 04:43 AM 9/3/2006, Kent Johnson wrote: >Dick Moores wrote: > > http://docs.python.org/lib/module-random.html says, > > > > "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()." > > > > >>> from random import shuffle, random > > >>> lst = ["a", "b", "c", "d"] > > >>> shuffle(lst) > > >>> lst > > ['c', 'b', 'd', 'a'] > > >>> shuffle(lst, random) > > >>> lst > > ['d', 'c', 'b', 'a'] > > >>> > > > > I can't see that shuffle(a) is any different from shuffle(a, > random). Is it? And > > how? > > >The docs say that shuffle(a) *is* the same as shuffle(a, random). If you >don't supply a second argument, the function random() is used. So >passing random as the second arg is the same as omitting the second arg. > >One reason to provide your own random function would be if you have one >that is more random than the standard function, for example os.urandom() >or a function based on an external random source such as >http://www.fourmilab.ch/hotbits/. The random number generator in Python >(Mersenne twister) is very high quality but that hasn't always been the >case and it is still deterministic. > >You might be interested in the Wikipedia article: >http://en.wikipedia.org/wiki/Random_number_generator >http://en.wikipedia.org/wiki/Mersenne_twister > >Trying the two versions once each, getting different results and saying >you can't see that they are different is...an interesting approach :-)
Well, sure it's stupid if you know what "supplying your own random function in place of random.random()" means. I do now, thanks to you and Alan Gauld. >But seriously, even with a poor random function you would have to call >shuffle many times and analyze the entire body of results carefully to >see any problem. Because I'm content with the pseudo-randomness supplied by the current random.random(), I won't pursue my questions about that 2nd argument of shuffle() any longer. Thanks to all, Dick Moores _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
