On 2019-06-24 09:23, Chris Angelico wrote:> On Mon, Jun 24, 2019 at 6:03
PM Andrew Barnert <abarn...@yahoo.com> wrote:
>>
>> On Sunday, June 23, 2019, 10:13:07 PM PDT, Chris Angelico
<ros...@gmail.com> wrote:
>>
>> > The biggest problem with this proposal is the way that, being a
>> > syntactic construct, it's going to be non-composable.
>>
>> > # Oops, syntax error
>> > with (some_expr as q,
>> > some_other_expr as w):
>> > pass
>>
>> I don't understand. Are you suggesting that some_expr could be
something like "2 if cond else pass", so if not cond, this is supposed
to be equivalent to "with ( as q, some_other_expr as w):", which is a
SyntaxError (at runtime)? If so, that's the same problem as with most
other syntactic locations where an expression can go, like the
assignment example I gave earlier.
>>
>
> Sorry, I kinda glossed over a lot of details there.
>
> The example that I gave is a SyntaxError, unrelated to the current
> proposal. To make it work, you have to remove the parens, and use a
> backslash to continue the line. And every now and then, someone
> proposes to make the 'with' statement accept the form I gave, because
> it would be cleaner. It isn't an easy change, because "with expr as
> name" is a syntactic construct; the "expr as name" part cannot be
> composed into a larger expression.
>
> The proposed syntax would have the exact same problem:
>
> stuff = [
> foo unless True,
> bar unless False,
> (quux("spam", "eggs", "sausage", "spam")
> unless customer_wants("spam"))
> ]
>
> This particular example would work if you just removed the parens (it
> doesn't need a backslash to continue the line, since it's inside a
> list display), but I can pretty much guarantee that people will put
> parens around one of these sequences and then wonder why on earth it
> doesn't work.
>
Well, I suppose it could work with parentheses, but not necessarily in
the way you want/expect. If customer_wants("spam") returns False, then
(quux("spam", "eggs", "sausage", "spam") unless customer_wants("spam"))
could mean ()! (You could say that it doesn't, and if you want that
behaviour then you should add a trailing comma.)
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