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Title: Add support for partial keyword arguments in extension functions
Type: enhancement Stage: resolved
Components: Argument Clinic, Interpreter Core Versions: Python 3.6
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: serhiy.storchaka Nosy List: larry, martin.panter, python-dev, rhettinger, serhiy.storchaka
Priority: normal Keywords: patch

Created on 2016-02-03 21:44 by serhiy.storchaka, last changed 2022-04-11 14:58 by admin. This issue is now closed.

File name Uploaded Description Edit
pyarg_parse_positional_only_and_keywords.patch serhiy.storchaka, 2016-02-09 14:01 review
pyarg_parse_positional_only_and_keywords_2.patch serhiy.storchaka, 2016-05-02 12:20 review
zlib_compress_positional_only_data.patch serhiy.storchaka, 2016-05-02 12:23 review
pyarg_parse_positional_only_and_keywords_3.patch serhiy.storchaka, 2016-05-08 14:58 review
Messages (10)
msg259521 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-02-03 21:44
Currently extension functions either accept only positional-only arguments (PyArg_ParseTuple), or keyword arguments (PyArg_ParseTupleAndKeywords). While adding support passing by keywords looks good for some arguments, for other arguments it doesn't make much sense. For example "encoding" and "errors" arguments for str or "base" argument for int are examples of good keyword arguments, but it is hard to choose good name for the first argument.

I suggest to allow to add the support of keyword arguments only for the part of arguments, while left other arguments positional-only. This issue consists from two stages:

1. Allow PyArg_ParseTupleAndKeywords to accept empty string "" as keywords and interpret this as positional-only argument.

2. Make Argument Clinic to generate code for partial keyword arguments. The syntax already supports this: "/" separates positional-only arguments from keyword arguments.
msg259525 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2016-02-04 02:22
For the examples you gave, they already seem to support keywords for the first parameter: int(x=0), str(object=""), bytes(source=b""). Maybe it is a bit unfortunate that they are inconsistent, but these names seem reasonable when considered separately.

But I agree that in those cases having the option of a keyword would rarely be useful. This proposal sounds like it could give a small benefit, and I guess it wouldn’t be costly to implement.
msg259773 - (view) Author: Raymond Hettinger (rhettinger) * (Python committer) Date: 2016-02-07 09:31
+1 for this suggestion.  There are a number of places where we've been trapped between having no keyword arguments or having to use keywords for all arguments even when it doesn't make sense to have all arguments be keywords.
msg259933 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-02-09 14:01
Proposed patch adds support for positional-only parameters in PyArg_ParseTupleAndKeywords(). It is simple, the most complex part is generating detailed error message for the case of calling with insufficient number of positional arguments.
msg264639 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-02 12:20
Removed development code from tests (thanks Martin for catching this) and adds support in Argument Clinic. Now the patch is complete and ready for final review.
msg264640 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-02 12:23
For example here is a patch that partially reverts issue26243 by making "data" positional parameter, but keeping "level" positional-or-keyword parameter.
msg264972 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-06 12:48
If there are no objections I'm inclined to commit pyarg_parse_positional_only_and_keywords_2.patch in short time.
msg265120 - (view) Author: Martin Panter (martin.panter) * (Python committer) Date: 2016-05-08 09:35
I made some suggestions in the documentation. I only skimmed over the C and arg clinic code, but there is nothing obviously wrong.
msg265143 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-08 14:58
On new patch applied Martin's suggestions, added entities in What's New and NEWS, added a reference to the glossary, and improved error message.
msg268141 - (view) Author: Roundup Robot (python-dev) (Python triager) Date: 2016-06-10 18:47
New changeset 69c0aa8a8185 by Serhiy Storchaka in branch 'default':
Issue #26282: PyArg_ParseTupleAndKeywords() and Argument Clinic now support
Date User Action Args
2022-04-11 14:58:27adminsetgithub: 70470
2016-06-10 18:55:30serhiy.storchakasetstatus: open -> closed
resolution: fixed
stage: patch review -> resolved
2016-06-10 18:47:43python-devsetnosy: + python-dev
messages: + msg268141
2016-05-08 14:58:35serhiy.storchakasetfiles: + pyarg_parse_positional_only_and_keywords_3.patch

messages: + msg265143
2016-05-08 09:35:53martin.pantersetmessages: + msg265120
2016-05-06 12:48:13serhiy.storchakasetassignee: serhiy.storchaka
messages: + msg264972
2016-05-02 12:23:10serhiy.storchakasetfiles: + zlib_compress_positional_only_data.patch

messages: + msg264640
2016-05-02 12:20:05serhiy.storchakasetfiles: + pyarg_parse_positional_only_and_keywords_2.patch

messages: + msg264639
components: + Interpreter Core, Argument Clinic
stage: patch review
2016-04-12 08:42:18ncoghlanlinkissue26729 dependencies
2016-02-12 18:15:12anish.shahsetnosy: - anish.shah
2016-02-09 14:01:34serhiy.storchakasetfiles: + pyarg_parse_positional_only_and_keywords.patch
keywords: + patch
messages: + msg259933
2016-02-07 09:31:29rhettingersetnosy: + rhettinger
messages: + msg259773
2016-02-04 07:43:02anish.shahsetnosy: + anish.shah
2016-02-04 02:22:28martin.pantersetmessages: + msg259525
2016-02-03 21:44:16serhiy.storchakacreate