reduce()--what is it good for?

Anton Vredegoor anton at
Sat Nov 8 14:36:19 CET 2003

Alex Martelli <aleaxit at> wrote:

>Of course you can memoize any pure function of hashable args.  But
>memoizing a recursive implementation of factorial has a nice property, 
>shared by other int functions implemented recursively in terms of their 
>values on other ints, such as fibonacci numbers: the memoization you do for 
>any value _helps_ the speed of computation for other values.  This nice 
>property doesn't apply to non-recursive implementations.

Maybe we need a better example because it is possible to use reduce on
a function which has side effects.


class _Memo: 
    biggest = 1
    facdict = {0 : 1, 1 : 1}

def fac(n):
    def mymul(x,y):
        res = x*y
        _Memo.facdict[y] = res
        _Memo.biggest = y
        return res        
    def factorial(x):
        b = _Memo.biggest
        if x > b: return reduce(mymul, xrange(b+1,x+1), b)
        return _Memo.facdict[x]
    return factorial(n)

def test():
    print fac(5)

if __name__=='__main__':

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