Avoiding argument checking in recursive calls
Scott David Daniels
Scott.Daniels at Acm.Org
Wed Feb 11 07:57:18 CET 2009
Steven D'Aprano wrote:
> I sometimes write recursive functions like this simple factorial:
> def fact(n):
> if n < 0: raise ValueError
> if n = 0: return 1
> return fact(n-1)*n
>
> At the risk of premature optimization, I wonder if there is an idiom for
> avoiding the unnecessary test for n <= 0 in the subsequent recursive
> calls? For the sake of the argument, let's pretend the test is expensive
> and I have a good reason for wanting to avoid it on subsequent calls :)
How about:
def fact(n):
if n < 2:
if n < 0:
raise ValueError
return 1
return fact(n - 1) * n
But really, iteration is the solution to this, and avoiding the
right answer is a mistake. I couldn't resist fixing your test
so you do one less layer of recursion.
--Scott David Daniels
Scott.Daniels at Acm.Org
More information about the Python-list
mailing list