On 10/05/2021 12:43, Chris Angelico wrote:
On Mon, May 10, 2021 at 9:36 PM Steven D'Aprano <steve@pearwood.info> wrote:
On Mon, May 10, 2021 at 10:04:58AM +1000, Chris Angelico wrote:
Is there an aim beyond saving two characters? It would remove a level of frustration. I've watched a lot of novice
On Mon, May 10, 2021 at 9:57 AM Steven D'Aprano <steve@pearwood.info> wrote: [...] 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