GeezerVison is showing github.com — Argument Clinic should understand *args and **kwargs parameters · Issue #64490 · python/cpython
Argument Clinic should understand *args and **kwargs parameters #64490Description
| BPO |
20291 |
| Nosy |
@rhettinger, @ncoghlan, @vstinner, @larryhastings, @methane, @meadori, @zware, @serhiy-storchaka, @GPHemsley, @isidentical, @Fidget-Spinner, @colorfulappl |
| PRs |
gh-64490: varargs support for argument clinic and refactor print with AC #18609bpo-20291: Fix MSVC warnings in getargs.c #27211gh-90350: Optimize builtin functions min() and max() #30286gh-64490: Fix bugs in argument clinic varargs processing #32092 |
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GitHub fields:
assignee = 'https://github.com/serhiy-storchaka'
closed_at = None
created_at = <Date 2014-01-18.01:55:25.863>
labels = ['type-feature', '3.7', 'expert-argument-clinic']
title = 'Argument Clinic should understand *args and **kwargs parameters'
updated_at = <Date 2022-03-24.08:27:39.531>
user = 'https://github.com/larryhastings' bugs.python.org fields:
activity = <Date 2022-03-24.08:27:39.531>
actor = 'colorfulappl'
assignee = 'serhiy.storchaka'
closed = False
closed_date = None
closer = None
components = ['Demos and Tools', 'Argument Clinic']
creation = <Date 2014-01-18.01:55:25.863>
creator = 'larry'
dependencies = []
files = []
hgrepos = []
issue_num = 20291
keywords = ['patch']
message_count = 10.0
messages = ['208380', '225514', '225531', '264959', '285642', '285647', '285654', '285660', '285779', '397721']
nosy_count = 12.0
nosy_names = ['rhettinger', 'ncoghlan', 'vstinner', 'larry', 'methane', 'meador.inge', 'zach.ware', 'serhiy.storchaka', 'gphemsley', 'BTaskaya', 'kj', 'colorfulappl']
pr_nums = ['18609', '27211', '30286', '32092']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue20291'
versions = ['Python 3.7'] Activitylarryhastings commented on Jan 18, 2014 ContributorAuthor More actions Argument Clinic currently prevents the "impl" function from ever seeing the "args" tuple or the "kwargs" dict. There should be a way to ask it to pass those values in to the "impl" function. larryhastings commented on Aug 19, 2014 ContributorAuthor More actions So, let's think about this for a minute. What's the API that we *want* here?
If your function has the signature
(a, b, c=20, *args)
and you call it with
(1, 2, 3, 4, 5)
should "args" be (4, 5), or (1, 2, 3, 4, 5)?
I assert that the impl function should get the same "args" (and "kwargs") that a Python function would--that is, post-argument-processing. In the above example "args" should get (4, 5).
This might be somewhat painful to do in round 1, where we're still leveraging off PyArg_ParseTuple*. But in the future it'll be cheaper to do it this way. In any case, it's the right API, so that's what we should do.
(Adding Nick just to see if he agrees--he had a use case for *args in the builtin module.) ncoghlan commented on Aug 19, 2014 Yes, I agree we should follow the Python level semantics, and only capture the excess positional arguments. For the record, the four builtins I flagged as needing this in order to add introspection information:
__build_class__
- 2 positional only args, arbitrary additional args
- checks size with PyTuple_GET_SIZE
- uses PyTuple_GET_ITEM x2 + PyTuple_GetSlice to unpack
print
- only arbitrary position args, iterates and extracts using PyTuple_GetItem
- uses PyArg_ParseTupleAndKeywords with an empty tuple to extract the keyword-only args
min
max
- use a shared helper function min_max
- uses the args tuple directly if size > 1
- otherwise uses PyArg_UnpackTuple to extract the supplied iterable
- uses PyArg_ParseTupleAndKeywords with an empty tuple to extract the keyword-only args
- this "one arg means iterable" style API might need to be a special case...
serhiy-storchaka commented on May 6, 2016 I think at first step we can support var-positional parameter only when there are no other positional parameters, and var-keyword parameter only when there are no other keyword parameters. So print, max and dict.update will be supported, but __build_class__, map and functools.partial are not. serhiy-storchaka commented on Jan 17, 2017 I'll try to implement the support of var-positional parameters. rhettinger commented on Jan 17, 2017 In case it is helpful, here's my list of examples where the AC and existing signature objects are insufficiently expressive:
type(obj)
type(name, bases, mapping)
two different signatures depending on type
range(stop)
range(start, stop)
range(start, stop, step)
dict.pop(key[, default])
default of None has different meaning than missing default
which raises KeyError when the key is missing
itertools.permutations(iterable[, r])
where the absence of *r* implies r=len(iterable)bisect.bisect_right(a, x[, lo[, hi]]) -> index
where the absence of *hi* implies hi=len(a)
min(iterable, *[, default=obj, key=func]) -> value
min(arg1, arg2, *args, *[, key=func]) -> value
has two signatures depending on the number of
positional arguments and a keyword argument
only used in the first signature. It's implementation
is also shared with max().
dict() -> new empty dictionary
dict(mapping) -> new dictionary initialized from a mapping object's
(key, value) pairs
dict(iterable) -> new dictionary initialized as if via:
d = {}
for k, v in iterable:
d[k] = v
dict(**kwargs) -> new dictionary initialized with the name=value pairs
in the keyword argument list. For example: dict(one=1, two=2)
def sumseq(seq, a=0, b=None):
# Pure python code with nullable int
if b is None:
b = len(seq)
return sum(seq[a:b])vstinner commented on Jan 17, 2017 FYI I started to work on a different Argument Clinic enhancement, issue bpo-29299: "Argument Clinic: Fix signature of optional positional-only arguments". gpshead commented on Feb 7, 2023 #18609 appears to have added *args support, but it wasn't documented.
- Doc/howto/clinic.rst could use an update.
Reacted by Erlend E. Aasland gpshead commented on Feb 7, 2023 (unassigning since it isn't actively being worked on) @isidentical as FYI for the missing documentation. skirpichev commented on Aug 12, 2025 AA-Turner commented on Sep 1, 2025 I've had a stab at **kwds support, see #138344. It is an intentionally restricted implementation, only supporting METH_VARARGS|METH_KEYWORDS and strictly positional-ponly parameters. However, I think it's a useful start, and allows converting several functions to AC already, which affords us the other benefits of using AC for those functions.
A Reacted by Erlend E. Aasland serhiy-storchaka commented on Aug 22, 2026 cmaloney commented on Oct 30, 2026
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