Avoiding argument checking in recursive calls

[andrew cooke]

Terry Reedy wrote:
> Reverse the test order
>
> def fact(n):
>      if n > 0: return fact(n-1)*n
>      if n == 0: return 1
>      raise ValueError

sweet!  but is this generally possible?  ie: did you think this up for
this question or is it an idiom that you find yourself using often?

andrew