map

[Gabriel Genellina]

En Mon, 31 Aug 2009 05:43:07 -0300, Hendrik van Rooyen  
<hendrik at microcorp.co.za> escribió:
> On Monday 31 August 2009 06:55:52 elsa wrote:
>
>> (Ultimately, I want to call myFunc(myList[0], 'booHoo'), myFunc(myList
>> [1], 'booHoo'), myFunc(myList[2], 'booHoo') etc. However, I might want
>> to call myFunc(myList[0], 'woo'), myFunc(myList[1], 'woo'), myFunc
>> (myList[2], 'woo') some other time).
>
> Here is some heretical advice:
>
> Do not use stuff like map and reduce unless they fit what you want to do
> perfectly, and "JustWorks" the first time.

I think of that advice as "orthodox", not "heretical"! (functional guys  
are minority here...)

> You have a very clear idea of what you want to do, so why do you not just
> simply write something to do it?
>
> something like this (untested):
>
> def woofer(thefunc,thelist,thething):
> 	theanswers = []
> 	for x in thelist:
> 		theanswers.append(thefunc(x,thething))
> 	return theanswers
>
> And the advantage is that you do not have to remember what map does...

This block:

	theanswers = []
	for x in thelist:
		theanswers.append(thefunc(x,thething))

is formally the same as this one:

	theanswers = [thefunc(x,thething) for x in thelist]

but the list comprehension is faster. So the function becomes:

def woofer(thefunc,thelist,thething):
	return [thefunc(x,thething) for x in thelist]

and may be inlined (it's usually easier to read).

> *ducks away from the inevitable flames*

*fights back to back with you against heretics*

-- 
Gabriel Genellina