using "private" parameters as static storage?

[Steven D'Aprano]

On Thu, 13 Nov 2008 19:52:13 -0700, Joe Strout wrote:

> Pity there isn't a way for a function to get a reference to itself
> except by name.  Still, when you rename a method, you're going to have
> to update all the callers anyway -- updating a couple of extra
> references within the method is not that much extra effort.

I have come across a situation where this was a problem.

I was writing a bunch of different versions of the classic factorial and 
Fibonacci functions, some iterative, some recursive, some with caches, 
and some without. What I wanted to do was do something like this (for 
factorial):


def iterative_without_cache(n):
    product = 1
    for i in xrange(1, n+1):
        product *= i
    return product

iterative_with_cache = decorate_with_cache(iterative_without_cache)

which works. But it doesn't work for the recursive version:

def recursive_without_cache(n):
    if n <= 1:
        return 1
    else:
        return n*recursive_without_cache(n-1)

recursive_with_cache = decorate_with_cache(recursive_without_cache)

for obvious reasons. Solution: the copy-and-paste anti-pattern. Good 
enough for test code, not for real work.

Now multiply the above by about a dozen slightly different recursive 
versions of the Fibonacci function, and you will see why it was a problem.


-- 
Steven