On Mon, May 10, 2021 at 9:36 PM Steven D'Aprano <st...@pearwood.info> wrote:
>
> 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 <st...@pearwood.info> 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.
>
What if the parens could be omitted only if there's no 'as' clause?
That eliminates the ambiguity. Is it really necessary to clarify what
"except TypeError, ValueError:" means, either to the interpreter or to
another programmer? Every objection has been based on the confusion of
"except TypeError, ValueError as e:", and I agree with that.
ChrisA
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