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[Python-ideas] Provide a 'key' argument for all() and any() builtins

Giampaolo Rodolà g.rodola at gmail.com
Mon Jul 23 13:28:08 CEST 2012 
2012/7/23 Chris Rebert <pyideas at rebertia.com>
>
> On Sun, Jul 22, 2012 at 9:03 PM, Giampaolo Rodolà <g.rodola at gmail.com> wrote:
> > This would be similar to 'key' argument already available for min(), max()
> > and sorted() and would let user decide what must be considered True and what
> > not.
> > Some use cases:
> >
> >
> > all(a, b, c, ... key=callable)
>
> You're missing some brackets or parens there:
>     all([a, b, c, ...], key=callable)
>
> <snip>
> > Thoughts?
>
> I see negligible advantage over just writing the generator expression directly:
>     all(callable(item) for item in iterable)

<snip>

> min() & max() return the result object satisfying the constraint, so
> the `key` argument makes sense for when you want to e.g. find the
> cheapest house rather than the price of the cheapest house.
> In contrast, any() & all() *always* just return a simple bool result,
> not the object whose truthiness determined the predicate's result, so
> `key` would be pointless since the result gets converted to a plain
> bool anyway (or at least, we can conceptualize the implementation as
> if it worked that way).


Agreed.
Please ignore my proposal then.

--- Giampaolo
 https://code.google.com/p/pyftpdlib/
https://code.google.com/p/psutil/
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