On Tue, Oct 30, 2007 at 11:37:57AM -0700, [EMAIL PROTECTED] wrote regarding Re: Iteration for Factorials: > > On Oct 30, 10:25 am, "J. Clifford Dyer" <[EMAIL PROTECTED]> wrote: > > On Tue, Oct 30, 2007 at 01:09:38PM +0100, Boris Borcic wrote regarding Re: > > Iteration for Factorials: > > > > > > > > > Py-Fun wrote: > > > > I'm stuck trying to write a function that generates a factorial of a > > > > number using iteration and not recursion. Any simple ideas would be > > > > appreciated. > > > > > fact = lambda n : len(map([1].__imul__,range(1,n+1))[0]) > > > > OK. Now I've been sucked in. How about this: > > > > def fact(x): > > def f(x): > > if int(x) != x: > > raise ValueError > > elif x > 1: > > return f(x-1) ** x > > elif x == 1: > > return 10 > > else: > > raise ValueError > > return len(str(f(x))) -1 > > > > The great part about this recursive solution is that you don't have to > > worry about the stack limit because performance degrades so quickly on the > > conversion to string! fact(8) takes a little less than a second, fact(9) > > takes about a minute, and fact(10) takes more time than I had patience to > > wait for! > > And the not-so-great part is that it raises an exception > on fact(0) which makes it utterly useless for calculating > combinations of m things taken n at a time: m!/n!*(m-n)! > > Why is it that no one seems able to get this right? >
I can't speak for everyone, but my excuses are as follows: * I haven't studied math or done math-heavy work in 8 years. * I'm not at my home computer, and most of the thread (wherein, I now recall, that particular rule was specified) is downloaded to my home computer, so I was working from my feeble memory. * I didn't care enough to google for it. That said, s/elif x == 1:/elif x in (0,1):/ should solve the problem -- http://mail.python.org/mailman/listinfo/python-list
