On Apr 27, 9:22 pm, Steven D'Aprano <ste...@remove.this.cybersource.com.au> wrote: > On Mon, 27 Apr 2009 20:27:07 -0700, William Clifford wrote: > > For some reason I thought I needed this code, but it turns out I don't, > > really. > > I need something weirder. Anyway, maybe someone else could use this. > > > def enrag(start, stop=None, step=1): > > '''Yield a range of numbers from inside-out, evens on left.''' > > [snip code] > > Interesting. > > That's equivalent to a reverse followed by a Monge Shuffle. > > http://mathworld.wolfram.com/MongesShuffle.htmlhttp://en.wikipedia.org/wiki/Shuffling_playing_cards#Mongean_shuffle > > I wrote a similar function to do this: > > def monge_shuffle(deck): > if len(deck) % 2: # Odd number of items. > deck[:] = deck[0::2] + deck[1::2][::-1] > else: # Even number of items. > deck[:] = deck[1::2] + deck[0::2][::-1] > return deck > > >>> list(enrag(20)) > > [18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]>>> > monge_shuffle(range(20)[::-1]) > > [18, 16, 14, 12, 10, 8, 6, 4, 2, 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]>>> > list(enrag(203)) == monge_shuffle(range(203)[::-1]) > > True > > I'm curious what your "something weirder" was.
Thanks for the links! Funny, while I worked on this I didn't think of looking up card shuffling to see if there might be an algorithms for it. I didn't think enrag (or her sister garne) would be unique, but I didn't expect they could be useful either. Cool! I weirder I needed was to generate an Ulam spiral sequence like this: [4, 3, 2, 5, 0, 1, 7, 8, 9] I found a couple of ways, one of which I'm a somewhat happier with. -- William Clifford -- http://mail.python.org/mailman/listinfo/python-list
