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Title: Support more than 255 arguments
Type: enhancement Stage: resolved
Components: Interpreter Core Versions: Python 3.7
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: serhiy.storchaka Nosy List: Trundle, andersk, brett.cannon, davidben, loewis, python-dev, rhettinger, sebastinas, serhiy.storchaka
Priority: low Keywords: patch

Created on 2011-08-26 02:42 by andersk, last changed 2022-04-11 14:57 by admin. This issue is now closed.

File name Uploaded Description Edit
issue12844_arbitrary_arguments.diff Trundle, 2011-09-02 22:00 review
no-args-limit.patch serhiy.storchaka, 2016-11-25 09:27 review
Pull Requests
URL Status Linked Edit
PR 552 closed dstufft, 2017-03-31 16:36
Messages (11)
msg142995 - (view) Author: Anders Kaseorg (andersk) * Date: 2011-08-26 02:42
This feels like an arbitrary restriction (obvious sequences have been replaced with ‘…’ to save space in this report):

>>> zip([0], [1], [2], …, [1999])
  File "<stdin>", line 1
SyntaxError: more than 255 arguments

especially when this works:

>>> zip(*[[0], [1], [2], …, [1999]])
[(0, 1, 2, …, 1999)]

Apparently that limit bites some people:

The bytecode format doesn’t support directly calling a function with more than 255 arguments.  But, it should still be pretty easy to compile such function calls by desugaring
  f(arg0, …, arg999, k0=v0, …, k999=v999)
  f(*(arg0, …, arg999), **{'k0': 'v0', …, 'k999': 'v999'})
msg142996 - (view) Author: Anders Kaseorg (andersk) * Date: 2011-08-26 02:56
I guess the desugaring is slightly more complicated in the case where the original function call already used *args or **kwargs:
  f(arg0, …, arg999, *args, k0=v0, …, k999=v999, **kwargs)
becomes something like
  f(*((arg0, …, arg999) + args),
    **dict({'k0': 'v0', …, 'k999': 'v999'}, **kwargs))
msg142998 - (view) Author: Raymond Hettinger (rhettinger) * (Python committer) Date: 2011-08-26 03:28
On python-dev a few month ago, Guido agreed with you that this is an arbitrary limitation that should be removed at some point.  In particular, he worried that programmatically generated code would tend to run into this limitation.
msg143002 - (view) Author: Martin v. Löwis (loewis) * (Python committer) Date: 2011-08-26 07:42
The approach looks fine to me. Would you like to work on a patch?
msg143440 - (view) Author: Andreas Stührk (Trundle) * Date: 2011-09-02 22:00
Attached is a patch that removes the limit and that allows passing an arbitrary number of positional and keyword arguments. Lacks tests for now.
msg143451 - (view) Author: David Benjamin (davidben) Date: 2011-09-03 03:32
I don't think that patch works. Consider a dict subclass which has overridden update. Or perhaps a list subclass which has overridden addition. It would be quite poor if Python's behavior here w.r.t. which overrides are followed switched as you added more arguments.
msg281655 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-11-24 21:33
Since issue27213 the bytecode no longer have a limitation for numbers of positional or keyword arguments.
msg281688 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-11-25 09:27
No longer changes to Python/compile.c are needed. Here is a patch against 3.7 that just removes the limit of the number of passed arguments in Python/ast.c and adds tests.

But still there is a limitation on the number of function parameters. It is caused by using a bytes objects as co_cell2arg.
msg281836 - (view) Author: Brett Cannon (brett.cannon) * (Python committer) Date: 2016-11-27 21:32
Patch LGTM.
msg281848 - (view) Author: Roundup Robot (python-dev) (Python triager) Date: 2016-11-28 08:52
New changeset 5c1bb72c0f5d by Serhiy Storchaka in branch 'default':
Issue #12844: More than 255 arguments can now be passed to a function.
msg281855 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-11-28 10:25
Thanks Brett.

See issue18896 for supporting functions with more than 255 parameters.
Date User Action Args
2022-04-11 14:57:21adminsetgithub: 57053
2017-03-31 16:36:20dstufftsetpull_requests: + pull_request943
2016-11-28 10:25:17serhiy.storchakasetstatus: open -> closed
resolution: fixed
messages: + msg281855

stage: commit review -> resolved
2016-11-28 08:52:21python-devsetnosy: + python-dev
messages: + msg281848
2016-11-27 21:32:20brett.cannonsetassignee: serhiy.storchaka
messages: + msg281836
stage: patch review -> commit review
2016-11-25 09:27:13serhiy.storchakasetfiles: + no-args-limit.patch

stage: patch review
messages: + msg281688
versions: + Python 3.7
2016-11-24 21:33:19serhiy.storchakasetnosy: + serhiy.storchaka
messages: + msg281655
2011-09-08 17:06:25sebastinassetnosy: + sebastinas
2011-09-03 03:32:07davidbensetnosy: + davidben
messages: + msg143451
2011-09-02 22:00:37Trundlesetfiles: + issue12844_arbitrary_arguments.diff

nosy: + Trundle
messages: + msg143440

keywords: + patch
2011-08-30 17:34:32brett.cannonsetnosy: + brett.cannon
2011-08-26 07:42:24loewissetnosy: + loewis
messages: + msg143002
2011-08-26 03:28:33rhettingersetpriority: normal -> low
nosy: + rhettinger
messages: + msg142998

2011-08-26 02:56:52andersksetmessages: + msg142996
2011-08-26 02:42:57anderskcreate