*args regression

[o11c]

BPO	24791
Nosy	@ncoghlan, @larryhastings, @benjaminp, @zware, @1st1, @o11c
Files	issue24791.patch

^{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 2015-08-05.22:01:00.775>
created_at = <Date 2015-08-05.03:42:24.872>
labels = ['interpreter-core', 'type-bug', 'release-blocker']
title = '*args regression'
updated_at = <Date 2015-10-04.03:03:41.344>
user = 'https://github.com/o11c'

bugs.python.org fields:

activity = <Date 2015-10-04.03:03:41.344>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2015-08-05.22:01:00.775>
closer = 'yselivanov'
components = ['Interpreter Core']
creation = <Date 2015-08-05.03:42:24.872>
creator = 'o11c'
dependencies = []
files = ['40128']
hgrepos = []
issue_num = 24791
keywords = ['patch', '3.4regression']
message_count = 10.0
messages = ['248014', '248015', '248016', '248017', '248018', '248020', '248044', '248082', '248083', '252251']
nosy_count = 7.0
nosy_names = ['ncoghlan', 'larry', 'benjamin.peterson', 'python-dev', 'zach.ware', 'yselivanov', 'o11c']
pr_nums = []
priority = 'release blocker'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24791'
versions = ['Python 3.5', 'Python 3.6']

[o11c]

The following code is allowed by the grammar of Python 3.4, but not Python 3.5:

def f(): g(*a or b)

where unary * has the lowest precedence, i.e. it is equivalent to:

def f(): g(*(a or b))

The cause of the regression that the 3.4 grammar for arglist uses '*' test but the 3.5 grammar uses '*' expr. This is likely an oversight due to the PEP-448 changes; the fix should most likely be applied to the new displays as well as fixing the regression.

---

Thanks to zware on IRC for actually testing this for me, since I don't have a runnable python3.5, just docs.

[o11c]

Related: bug 24176 fixed this for the ** case.

[python-dev]

New changeset 3c170f68407f by Zachary Ware in branch '3.4':
Issue bpo-24791: Add tests for things that regressed with PEP-448
https://hg.python.org/cpython/rev/3c170f68407f

[zware]

Test committed on 3.4; I'm not comfortable enough with the grammar to actually fix the issue (the obvious change of star_expr => '*' test isn't enough, I tried :)).

[1st1]

The attached patch should fix that. Please review.

[o11c]

Also consider:

*() or (), *() or ()
[() or (), *() or ()]
{() or (), *() or ()}
{**{} or {}, **{} or {}}

Note that the second-or-later argument is a separate part of the grammar so that's why I wrote it twice.

Actually, I think star_expr will probably go away entirely.

[1st1]

Actually, I think star_expr will probably go away entirely.

I'm not so concerned with supporting [*[] or []] stuff, but rather fixing the immediate regression in 3.5.0. I'd keep the patch size to the minimum.

[python-dev]

New changeset e4cb64628673 by Yury Selivanov in branch '3.5':
Issue bpo-24791: Fix grammar regression for call syntax: 'g(*a or b)'.
https://hg.python.org/cpython/rev/e4cb64628673

New changeset 4c89dd5199e5 by Yury Selivanov in branch 'default':
Merge 3.5 (issue bpo-24791)
https://hg.python.org/cpython/rev/4c89dd5199e5

[python-dev]

New changeset 40c391d12741 by Yury Selivanov in branch '3.5':
Issue bpo-24791: More tests in test_parser
https://hg.python.org/cpython/rev/40c391d12741

New changeset a572137b4f05 by Yury Selivanov in branch 'default':
Merge 3.5 (issue bpo-24791; more tests in test_parser)
https://hg.python.org/cpython/rev/a572137b4f05

[python-dev]

New changeset 20e0906a808e by Terry Jan Reedy in branch '3.5':
Issue bpo-24791: Escape rst markup char in NEWS entry to avoid Sphinx warning.
https://hg.python.org/cpython/rev/20e0906a808e