In function call, keyword arguments could follow *args

[amauryfa]

BPO	3473
Nosy	@warsaw, @birkenfeld, @rhettinger, @terryjreedy, @mjpieters, @jcea, @amauryfa, @ncoghlan, @benjaminp
Files	kwargs30.patch kwargs26.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 = 'https://github.com/amauryfa'
closed_at = <Date 2008-08-19.19:53:03.394>
created_at = <Date 2008-07-31.01:16:30.124>
labels = []
title = 'In function call, keyword arguments could follow *args'
updated_at = <Date 2014-08-28.04:07:25.212>
user = 'https://github.com/amauryfa'

bugs.python.org fields:

activity = <Date 2014-08-28.04:07:25.212>
actor = 'python-dev'
assignee = 'amaury.forgeotdarc'
closed = True
closed_date = <Date 2008-08-19.19:53:03.394>
closer = 'benjamin.peterson'
components = []
creation = <Date 2008-07-31.01:16:30.124>
creator = 'amaury.forgeotdarc'
dependencies = []
files = ['11010', '11011']
hgrepos = []
issue_num = 3473
keywords = ['patch']
message_count = 17.0
messages = ['70449', '70451', '70485', '70499', '70502', '70510', '70597', '71094', '71198', '71293', '71471', '71473', '71481', '71486', '72485', '225968', '226009']
nosy_count = 10.0
nosy_names = ['barry', 'georg.brandl', 'rhettinger', 'terry.reedy', 'mjpieters', 'jcea', 'amaury.forgeotdarc', 'ncoghlan', 'benjamin.peterson', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'accepted'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue3473'
versions = ['Python 3.0']

[amauryfa]

functions with keyword-only arguments have this form:
def f(x, *args, y):
pass
parameters can appear after the *arg, they are required to be passed by
keyword.

It would be more consistent to allow this function call:
f(X, *ARGS, y=Y)
This is invalid syntax, *ARGS is required to be at the end of the
arguments, together with an eventual **KWARGS. This restriction should
be lifted.

See the use case in
http://mail.python.org/pipermail/python-3000/2008-July/014437.html

[amauryfa]

Should this apply to 2.6 as well? See r65321, I find the last line
easier to read when arguments are in this order.

    def grouper(n, iterable, fillvalue=None):
        args = [iter(iterable)] * n
        return izip_longest(*args, fillvalue=fillvalue)

On the cons side, keyword-only arguments don't exist in 2.6, so the
consistency with function definition syntax does not apply.

[rhettinger]

+1 for applying to 2.6.

izip_longest() is a perfect example of where it's important.

[amauryfa]

Patches for both versions are attached.

[benjaminp]

The patches look good to me.

[ncoghlan]

I'll have a look at this in the next day or two.

[amauryfa]

I will not have internet access for the next week.
Raymond, would you take care of this issue?

[terryjreedy]

Another use case: upon reading A.Baxter's Porting to 3 talk, I realized,
slightly generalizing from his example, that
print(s.join(map(str,it))) == print(*it,sep=s) -- or would, except that
it currently has to be written non-intuitively as print(sep=s,*it),
which I might not have tried except for knowing about this issue.

Given that many have problems with .join and that most uses are to
produce immediate output not otherwise processed, I think having the
replacement work in the way many would expect would be a win.
So I hope this makes the next beta.

[birkenfeld]

Ping!

[amauryfa]

Barry, is it still time for this to be included in 2.6b3?
Guido already approved the idea:
http://mail.python.org/pipermail/python-3000/2008-July/014506.html

[warsaw]

Guido's approved it, so please go ahead and add it before beta 3.

[benjaminp]

Applied for 2.6 in r65872.

[benjaminp]

Done for py3k in r65877.

[benjaminp]

Now test_compiler is breaking for us because the compiler package can't
handle the change.

[amauryfa]

The compiler package was fixed some time ago with r65891

[mjpieters]

The documentation change in this patch introduced a bug in the Call grammar:

| "" expression ["," "" expression] ["," "**" expression]

instead of

| "*" expression ["," keyword_arguments] ["," "**" expression]

giving the impression that *expression is allowed twice.

[python-dev]

New changeset 3ae399c6ecf6 by Benjamin Peterson in branch '2.7':
correct call grammar error (bpo-3473)
http://hg.python.org/cpython/rev/3ae399c6ecf6