Description

pablogsal

opened on Feb 11, 2022

Issue body actions

BPO	46725
Nosy	@gvanrossum, @terryjreedy, @jwilk, @serhiy-storchaka, @JelleZijlstra, @lysnikolaou, @pablogsal, @miss-islington, @isidentical, @erlend-aasland
PRs	bpo-46725: Document starred expressions in for statements #31481

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2022-02-22.18:31:20.414>
created_at = <Date 2022-02-11.18:10:30.648>
labels = ['interpreter-core', '3.9', '3.10', '3.11']
title = 'Unpacking without parentheses is allowed since 3.9'
updated_at = <Date 2022-02-22.18:31:20.413>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2022-02-22.18:31:20.413>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2022-02-22.18:31:20.414>
closer = 'pablogsal'
components = ['Parser']
creation = <Date 2022-02-11.18:10:30.648>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 46725
keywords = ['patch']
message_count = 11.0
messages = ['413089', '413090', '413091', '413092', '413098', '413101', '413501', '413507', '413698', '413703', '413718']
nosy_count = 10.0
nosy_names = ['gvanrossum', 'terry.reedy', 'jwilk', 'serhiy.storchaka', 'JelleZijlstra', 'lys.nikolaou', 'pablogsal', 'miss-islington', 'BTaskaya', 'erlendaasland']
pr_nums = ['31481']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46725'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Activity

1. pablogsal commented on Feb 11, 2022

   

   pablogsal

   on Feb 11, 2022

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   Seems that this is allowed since the PEG parser rewrite:

   for x in *a, *b:
       print(x)

   but I cannot find anywhere were we discussed this. I am not sure if we should keep it or treat it as a bug and fix it.
2. pablogsal

   added

   3.9 (EOL)end of lifeend of life

   3.10 (EOL)end of lifeend of life

   3.11only security fixesonly security fixes

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on Feb 11, 2022
3. isidentical commented on Feb 11, 2022

   

   isidentical

   on Feb 11, 2022

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   Since this was already allowed in 3.9 and 3.10 stable relases, and since it is consistent with the RHS of an assignment (something = *a, *b); I'd lean towards keeping it (and maybe fixing the old parser's grammar to reflect that) and documenting this.

   Reacted by Kreusada
4. JelleZijlstra commented on Feb 11, 2022

   

   JelleZijlstra

   on Feb 11, 2022

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   I'd lean towards keeping this syntax:

   • It's already been out for two releases, so there's user code out there relying on it. (In fact we found out about this because somebody complained that Black's parser couldn't handle this code.)
   • The syntax isn't obviously confusing and the meaning is clear.
   • It's not hard to parse; it was easy to adjust Black's parser to allow it.

   Reacted by William Andrea
5. erlend-aasland commented on Feb 11, 2022

   

   erlend-aasland

   on Feb 11, 2022

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   +1 (what Jelle said)
6. gvanrossum commented on Feb 11, 2022

   

   gvanrossum

   on Feb 11, 2022

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   Let's just document it for 3.11.

   Reacted by jmwielandt, Thomas Grainger, Vibhakar Solanki, Medardo Antonio Rodriguez, jh4mit, Jongwook Choi, Kolen Afix, Nikita Kurpas, Vishesh Panchal, Herman Beeksma and 1 more
7. pablogsal commented on Feb 11, 2022

   

   pablogsal

   on Feb 11, 2022

   MemberAuthor

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   Will prepare a PR
8. terryjreedy commented on Feb 18, 2022

   

   terryjreedy

   on Feb 18, 2022

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   Allowing no parentheses is also consistent with the following:
   for x in 1,2,3: print(x)
9. gvanrossum commented on Feb 18, 2022

   

   gvanrossum

   on Feb 18, 2022

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   Adding jwilk back (a bpo interaction with browser form caching makes this happen frequently).

   Reacted by Surya
10. serhiy-storchaka commented on Feb 22, 2022

    

    serhiy-storchaka

    on Feb 22, 2022

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    What exactly was happened? What rule was changed? Can it cause other changes which allow ambiguous code or change semantic?
11. pablogsal commented on Feb 22, 2022

    

    pablogsal

    on Feb 22, 2022

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    What happened is that the new grammar using the PEG parser used the equivalent of starred_testlist instead of testlist for the iterable list of for statements.

    The only extra thing allowed is starred elements, that are interpreted as if you are building a tuple without parentheses.
12. miss-islington commented on Feb 22, 2022

    

    miss-islington

    on Feb 22, 2022

    Contributor

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    New changeset 7fb94fd by Pablo Galindo Salgado in branch 'main':
    bpo-46725: Document starred expressions in for statements (GH-31481)
    7fb94fd
13. pablogsal

    closed this as completedon Feb 22, 2022
14. pablogsal

    closed this as completedon Feb 22, 2022
15. ezio-melotti

    transferred this issue fromon Apr 10, 2022

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