Static analysis and factorisation, I sub ! :D
Le mar. 11 mai 2021 à 01:47, Rob Cliffe via Python-ideas <
python-ideas@python.org> a écrit :
>
>
> On 10/05/2021 12:43, Chris Angelico wrote:
> > 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.
> >
> >
> +0.9. A practical solution, although it makes the language definition
> more complicated. Practicality beating purity.
> Rob Cliffe
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