[issue46725] Unpacking without parentheses is allowed since 3.9

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue46725] Unpacking without parentheses is allowed since 3.9

[miss-islington]

miss-islington  added the comment:


New changeset 7fb94fd7a88f14096a5094d8a979a3912672 by Pablo Galindo Salgado 
in branch 'main':
bpo-46725: Document starred expressions in for statements (GH-31481)
https://github.com/python/cpython/commit/7fb94fd7a88f14096a5094d8a979a3912672


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[issue46725] Unpacking without parentheses is allowed since 3.9

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

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.

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

What exactly was happened? What rule was changed? Can it cause other changes 
which allow ambiguous code or change semantic?

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
keywords: +patch
pull_requests: +29612
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/31481

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Guido van Rossum]

Guido van Rossum  added the comment:

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

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Terry J. Reedy]

Terry J. Reedy  added the comment:

Allowing no parentheses is also consistent with the following:
  for x in 1,2,3: print(x)

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Jakub Wilk]

Change by Jakub Wilk :


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nosy: +jwilk

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Will prepare a PR

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Guido van Rossum]

Guido van Rossum  added the comment:

Let's just document it for 3.11.

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Erlend E. Aasland]

Erlend E. Aasland  added the comment:

+1 (what Jelle said)

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Jelle Zijlstra]

Jelle Zijlstra  added the comment:

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.

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Batuhan Taskaya]

Batuhan Taskaya  added the comment:

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.

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[issue46725] Unpacking without parentheses is allowed since 3.9

[Pablo Galindo Salgado]

New submission from Pablo Galindo Salgado :

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.

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components: Parser
messages: 413089
nosy: BTaskaya, gvanrossum, lys.nikolaou, pablogsal
priority: normal
severity: normal
status: open
title: Unpacking without parentheses is allowed since 3.9
versions: Python 3.10, Python 3.11, Python 3.9

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