[Python-Dev] vox populii illiterati

[Gareth McCaughan]

Alex Martelli wrote, replying to ?!ing:

> Forms such as:
> 
>     [ f(23) for f in stuff if callable(f) ]
> 
> have been in Python for years now, and you could indeed
> say "the very first thing you see" (the call f(23)) is "getting
> short-circuited" by an if-guard at the very end.

I think one reason why that isn't so troublesome is that
you can think of it as doing the filtering first: it's the
same as

    [f(23) for f in [f for f in stuff if callable(f)]]

where the only "short-circuiting" is the trivial sort
equivalent to a call to "filter". Except that the unexpanded
form is shorter and clearer and avoids a gratuitous
list allocation, of course.

But, actually, I've always felt slightly queasy about the
syntax for filtering in listcomps, because of the way that
it interrupts the "right-to-left" dataflow. I'm not sure

    [f(23) if callable(f) for f in stuff]

is really any better, though. Maybe it should have been

    [for f in stuff: if callable(f): f(23)]

<0.5 tim>. Actually, I *like* that, because it makes the
behaviour of nested listcomps clearer. Oh well.

                           *

Speaking of filtering listcomps, am I unusual in thinking
it would be nice if you could say "[t in I if C]"
instead of "[t for t in I if C]" when all you want
is the filtering effect? I suspect I may be, since
the shorter form is less logical than the longer.
Perhaps the main reason why I want it is that it seems
to be what my fingers always type for me when I write
a filtering listcomp.

-- 
g