[Python-ideas] Inline assignments using "given" clauses
steve at pearwood.info
Fri May 11 07:46:27 EDT 2018
On Sat, May 05, 2018 at 06:24:07AM -0400, Juancarlo Añez wrote:
> I think that "expr as y" was discarded too quickly.
This discussion started back in *February*. I don't think "too quickly"
applies to ANYTHING about it.
And Chris' first draft of the PEP:
I have been one of the main proponents of "as". See, for example:
At least, I *was*. I'm now satisfied that "as" is the wrong solution,
and I don't think it was discarded too quickly. Even though it makes me
sad that "as" is not suitable, I'm satisfied that the problems with it
would require too high a price to solve.
The major problem is that it will clash with "except as" and "with as"
statements. Of course we *could* introduce some sort of special
treatment, possibly as simple as simply banning the use of binding-
assignments inside except/with statements, but such special rules add
complexity, make the feature less useful, harder to learn, and more
Allowing or disallowing particular expressions after a certain keywork
ought to be a last resort. Even though this was my preferred solution,
I've now come to change my mind and think this would have been a
(Thanks Chris for sticking to your guns and rejecting "as".)
> The special cases that may arise over "except" and "with" can be worked
> out and documented.
but there's no "may" about this. Using "as" does clash, it's not a
matter of whether or not it will clash, we know it will. And it's easy
to say that it "can" be worked out, but unless you have a concrete
proposal to work it out, that's not really an argument in favour for
"as", it is just a hope.
Guido has also correctly pointed out that will "as" is used to bind
names in other contexts, it doesn't *quite* work the same as regular =
assignment. Again, the "with" statement is especially relevant:
with expression as name
does not bind the value of the expression to name, except by
coincidence. It actually binds the value of expession.__enter__() to
I still, and probably always will, like the look of
result = (expression as spam) + spam**2
but I'm realistic to realise that it isn't practical.
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