Description

ned2

opened on Jan 31, 2023

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Feature

In Python 3.11, the except* was added for working with ExceptionGroups. The availability of ExceptionGroup itself will depend on #4247, but in the meantime, the following snippet is valid CPython 3.11 that currently throws a SyntaxError in RustPython:

try:
    print("yay")
except* Exception as e:
    print("oh no")

I discovered this while digging into some code that ruff cannot handle, which on the surface looks like a slightly different issue. The following snippet is valid CPython 3.11 but also throws a SyntaxError in RustPython:

my_dict = {}
my_dict[*"ab"] = 1

The expected behaviour is that the string should be unpacked and the value of the dict with key ('a','b') set to 1. In case that feels a little contrived, here's what I was doing at the time:

import typing
values = ["dog", "cat"]
Pets = typing.Literal[*values]

Python Documentation

The first incompatibility issue is clearly documented here, and called out under New syntax features in What’s New In Python 3.11.

However the second incompatibility is not documented in the changelog, and I did confirm that this was new in CPython 3.11, as the snippet throws a syntax error in 3.10.

I wonder if this was a (nice?) side-effect of the changes that were introduced to make except* work. There is a seemingly related precedent for this, where using * to unpack without parentheses in for statements was enabled via the PEG parser in CPython 3.9, but was not noticed then and only documented in 3.11.

Reacted by DimitrisJim

Reacted by Copilot

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1. DimitrisJim commented on Jan 31, 2023

   

   DimitrisJim

   on Jan 31, 2023

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   Unpacking in indexes was introduced with PEP 646 (specifically, see here). I guess it isn't documented in that section because it isn't new syntax per se, more of a change in where * is allowed (it probably should be in the Other Language Changes though, which also mentions another small syntax change).

   Reacted by William Andrea
2. ned2 commented on Jan 31, 2023

   

   ned2

   on Jan 31, 2023

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   ahhh nice yes, that's exactly it! turns out that is a hard document to find with Google. I certainly looked for it.

   yeah agreed, would have been good to see that in the Other Language Changes section
3. charliermarsh commented on Feb 21, 2023

   

   charliermarsh

   on Feb 21, 2023

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   Fixed :)

   Reacted by Ned Letcher
4. youknowone commented on Feb 21, 2023

   

   youknowone

   on Feb 21, 2023

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   resolved by @charliermarsh , thanks!
5. youknowone

   closed this as completedon Feb 21, 2023
6. youknowone

   reopened this on Feb 21, 2023
7. youknowone commented on Feb 21, 2023

   

   youknowone

   on Feb 21, 2023

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   I am sorry, the parser part is done but runtime is not.

   Reacted by Charlie Marsh
8. charliermarsh commented on Feb 21, 2023

   

   charliermarsh

   on Feb 21, 2023

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   Ah correct!
9. fanninpm commented on Feb 21, 2023

   

   fanninpm

   on Feb 21, 2023

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   cc @qingshi163 for inclusion in #4423
10. DimitrisJim commented on Feb 22, 2023

    

    DimitrisJim

    on Feb 22, 2023

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    let's break this up in two issues? they touch on different subjects and the unpacking might be a good issue for someone to tackle. (plus, the title doesn't make it obvious that the parsing part of this is solved but the runtime isn't)

    Reacted by Jeong, YunWon
11. youknowone

    added

    A-vmArea: virtual machineArea: virtual machine

    on Feb 22, 2023
12. youknowone

    assigned

    Copilot

    and

    youknowone

    on Dec 25, 2025
13. youknowone

    closed this as completedin #6530on Dec 26, 2025

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