On Mon, May 10, 2021 at 10:04:58AM +1000, Chris Angelico wrote:
> On Mon, May 10, 2021 at 9:57 AM Steven D'Aprano <[email protected]> wrote:
[...]
> > Is there an aim beyond saving two characters?
> It would remove a level of frustration. I've watched a lot of novice
> programmers, and some intermediate programmers, run into a source of
> (now completely unnecessary) pain that changing this:
>
> except ValueError:
>
> into this:
>
> except ValueError, TypeError:
>
> doesn't work. Yes, it's a quick SyntaxError,
You say it is completely unnecessary, but is it? The way `as` currently
works and the way this proposal will have it work are just different
enough to make me fret.
import spam, eggs, cheese, aardvark as hovercraft
with spam, eggs as f
except ValueError, KeyError, TypeError as err
How long will it be before people, fooled by the similarity to other
uses of `as`, try writing this:
except ValueError as verr, KeyError as kerr, TypeError as terr
and how soon after that before people propose it as an actual feature?
> but the editor won't show
> it up (since most editors are Python 2 compatible, and wouldn't be
> checking this level of syntax anyway), so there's X amount of time
> spent coding, then go to run the thing, and it won't work the way they
> expect it to.
"My editor doesn't recognise this error" is not a strong argument in
favour of a change that otherwise adds no new functionality.
> If it weren't for the Python 2 issues, would there be any good reason
> for demanding parentheses? We don't need them in a for loop:
>
> for i, thing in enumerate(stuff):
True, but we do need them here:
[1,x for x in range(3)]
even though there is only one possible interpretation of the code. It
can't be `[1, generator]` because the hypothetical generator expression
isn't parenthesized.
Sometimes we require parens as a "belts and braces" sort of thing.
There's no *actual* syntactic ambiguity, but we require the parens just
to be sure:
>>> a := len('abc')
File "<stdin>", line 1
a := len('abc')
^
SyntaxError: invalid syntax
>>> (a := len('abc'))
3
I feel the same about this proposal. Without the brackets grouping the
exceptions, it feels too close to binding only the last one in the group
rather than the entire tuple of exceptions.
--
Steve
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