Add keyword-only parameter support to PyArg_ParseTupleAndKeywords

[larryhastings]

BPO	14328
Nosy	@gpshead, @pitrou, @larryhastings, @benjaminp, @ericsnowcurrently
Files	larry.parsekwonly.diff.2.txt larry.parsekwonly.diff.3.txt larry.parsekwonly.diff.4.txt larry.parsekwonly.diff.5.txt larry.parsekwonly.diff.7.txt

^{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 = 'https://github.com/larryhastings'
closed_at = <Date 2012-03-20.20:08:02.518>
created_at = <Date 2012-03-15.21:49:18.370>
labels = ['interpreter-core', 'type-feature']
title = 'Add keyword-only parameter support to PyArg_ParseTupleAndKeywords'
updated_at = <Date 2012-03-20.20:08:02.517>
user = 'https://github.com/larryhastings'

bugs.python.org fields:

activity = <Date 2012-03-20.20:08:02.517>
actor = 'larry'
assignee = 'larry'
closed = True
closed_date = <Date 2012-03-20.20:08:02.518>
closer = 'larry'
components = ['Interpreter Core']
creation = <Date 2012-03-15.21:49:18.370>
creator = 'larry'
dependencies = []
files = ['24878', '24883', '24901', '24912', '24955']
hgrepos = []
issue_num = 14328
keywords = []
message_count = 16.0
messages = ['155961', '155964', '155965', '155966', '155968', '155979', '155987', '155998', '156060', '156145', '156186', '156361', '156362', '156376', '156377', '156454']
nosy_count = 7.0
nosy_names = ['gregory.p.smith', 'pitrou', 'larry', 'benjamin.peterson', 'Arfrever', 'python-dev', 'eric.snow']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue14328'
versions = ['Python 3.3']

[larryhastings]

This has been split off from bpo-14127 at Antoine's request.

The attached patch adds support for keyword-only arguments to the PyArg_ParseTupleAndKeywords() family of functions. Includes doc and test.

I used '$' to indicate "all parameters after this are keyword-only"; since they must also be optional it must follow a '|'. (I would have used '*' but we already use that for 'U*' 's* etc.)

The patch already received one review from Greg P. Smith on the previous issue; the patch I'm attaching here is the second revision incorporating his suggestions.

[benjaminp]

Why do you force them to be optional?

[larryhastings]

It frankly never occurred to me that you'd want mandatory keyword-only arguments. Implementing them as optional-only was easy; I'm not sure but making them possibly mandatory (or both!) might complicate matters.

Is there a use case for 'em?

[benjaminp]

2012/3/15 Larry Hastings <report@bugs.python.org>:

Larry Hastings <larry@hastings.org> added the comment:

It frankly never occurred to me that you'd want mandatory keyword-only arguments.  Implementing them as optional-only was easy; I'm not sure but making them possibly mandatory (or both!) might complicate matters.

Is there a use case for 'em?

No idea, but at some point we might want them and it parallels the
Python interface.

[larryhastings]

How about we leave it for now, and if we need it later we can fix the implementation. Adding that feature won't break existing calls--we'll just permit $ to occur before/without | in the format string.

[larryhastings]

BTW, I have the os.utime patch nearly ready for review; it works, it just needs doc and test. But it's dependent on this patch--and it'd be smoother if bpo-14127 were finished too. So I'll hold off on posting the new patch until the fates of these two are decided.

[benjaminp]

I want bpo-14325 to go in first.

[larryhastings]

Attached is r3 of my patch incorporated Benjamin's suggestions.

I want bpo-14325 to go in first.

Why do you care? If I get signoff before 14325 does please explain to me why I should wait. They don't touch the same lines; should be a clean merge no matter who goes first.

[benjaminp]

Shouldn't using vgetargs1 with '$' in the format string just be an error? vgetargs1 doesn't know anything about keyword arguments.

[larryhastings]

Shouldn't using vgetargs1 with '$' in the format string just be
an error? vgetargs1 doesn't know anything about keyword arguments.

Thank you for catching that! Serves me right for search-and-destroy style development--I'm not that familiar with getargs.c.

Fixed, which is to say I removed that gunk, in attached patch #4 against current trunk.

[larryhastings]

Incorporated the latest round of suggestions from Benjamin's most recent--and very thorough!--review. Thanks, Benjamin!

[larryhastings]

Anyone else? Or can I get the go-ahead?