Should any() and all() take a key= argument?

[Steven D'Aprano]

On Sat, 01 Apr 2006 08:12:25 -0300, Felipe Almeida Lessa wrote:

> Em Sáb, 2006-04-01 às 20:44 +1000, Steven D'Aprano escreveu:
>> Here's another way of doing it:
>> 
>> lst = [2, 4, 42]
>> any(map(lambda x: x==42, lst))
> 
> In fact, as we're talking about Python 2.5 anyway, it would be better
> not to waste memory and use:
> 
> any(x == 42 for x in lst)

You might be talking about Python 2.5, but I certainly am not. any()
and all() are easy to (almost) implement in earlier Python versions:

try:
    any
except NameError:
    # warning: this version will consume an iterator
    def any(seq):
        for s in seq:
            if s: return True
        return False

and similarly for all(). 

In any case, I question your assumption that the version using map must
automatically "waste memory". Iterators carry a certain amount of overhead
which lists do not. For small enough lists, that overhead will be smaller
than the extra memory used by the list. "Small enough" will depend on the
type of objects involved: big complex objects created on the fly by
the generator gives the generator the advantage, small simple objects
like ints give the list the advantage. As Python doesn't give us any way to
measure the memory used by an object, it is hard to say where that
cut-off lies, but my wild guess is that for ints, it would probably be in
the multiple tens.

But then, unless these are big complex objects, why are we
micro-optimizing our code anyway? I'm running a Python process, and
it is consuming 6.7MB of memory at the moment. Do I really care about
saving 80 or 100 bytes?, or even 100 kilobytes? I don't think so.



-- 
Steven.