Avoiding argument checking in recursive calls

[afriere at yahoo.co.uk]

On Feb 11, 1:48 pm, Jervis Whitley <jervi... at gmail.com> wrote:

> Hello, an idea is optional keyword arguments.
>
> def fact(n, check=False):
>   if not check:
>     if n < 0: raise ValueError
>   if n == 0: return 1
>   return fact(n - 1, check=True) * n
>
> essentially hiding an expensive check with a cheap one. It saves you
> duplicating code in a separate function like in your example.

Given the original read:

def fact(n):
    if n < 0: raise ValueError
    if n = 0: return 1
    return fact(n-1)*n

You've merely replaced the 'test n<0' with 'not check' at the expense
of an additional parameter that has to be passed each time (and the
additional test 'n<0' for the first iteration).