[issue37593] ast.arguments has confusing args/posonlyargs ordering

[Mairi Dulaney]

Mairi Dulaney  added the comment:

The patch that was merged to fix this may have caused a regresion in xonsh.  Am 
working on a reproducer.

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nosy: +mdulaney

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[Pablo Galindo Salgado]

Pablo Galindo Salgado  added the comment:

Thanks for the report, Benjamin!

--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[miss-islington]

miss-islington  added the comment:


New changeset cf9a63c6c7e19f3d27cf3b5731d02cc216ef3dd1 by Miss Islington (bot) 
in branch '3.8':
bpo-37593: Swap the positions of posonlyargs and args in the constructor of 
ast.parameters nodes (GH-14778)
https://github.com/python/cpython/commit/cf9a63c6c7e19f3d27cf3b5731d02cc216ef3dd1


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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[miss-islington]

Change by miss-islington :


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pull_requests: +14575
pull_request: https://github.com/python/cpython/pull/14779

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[miss-islington]

miss-islington  added the comment:


New changeset cd6e83b4810549c308ab2d7315dbab526e35ccf6 by Miss Islington (bot) 
(Pablo Galindo) in branch 'master':
bpo-37593: Swap the positions of posonlyargs and args in the constructor of 
ast.parameters nodes (GH-14778)
https://github.com/python/cpython/commit/cd6e83b4810549c308ab2d7315dbab526e35ccf6


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nosy: +miss-islington

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[Pablo Galindo Salgado]

Change by Pablo Galindo Salgado :


--
keywords: +patch
pull_requests: +14574
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/14778

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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nosy: +levkivskyi, pablogsal, serhiy.storchaka

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[issue37593] ast.arguments has confusing args/posonlyargs ordering

[Benjamin S Wolf]

New submission from Benjamin S Wolf :

Positional-only arguments come before position-or-keyword arguments.

def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):

However, the posonlyargs are defined to come after args in the AST:

arguments = (arg* args, arg* posonlyargs, arg? vararg, arg* kwonlyargs,
 expr* kw_defaults, arg? kwarg, expr* defaults)

which results in confusing ast.dump output because they share defaults:

>>> r = ast.parse('lambda a=1,/,b=2:a+b', mode='eval')
>>> ast.dump(r.body.args)
"arguments(
args=[arg(arg='b', annotation=None, type_comment=None)],
posonlyargs=[arg(arg='a', annotation=None, type_comment=None)],
vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None,
defaults=[Constant(value=1, kind=None), Constant(value=2, kind=None)])"
[manually prettified]

Note how the ordering is 'args b', then 'posonlyargs a', but the defaults are 
still 1 then 2. This can be confusing to someone building an ast.arguments 
using keywords because the elements in 'defaults' have to be supplied in a 
specific order, but the keyword args 'args' and 'posonlyargs' do not, or to 
someone building an ast.arguments using positional arguments (because, maybe 
ironically, they're not keyword-only arguments) because 'posonlyargs' and 
'args' must be supplied in a different order than the ordering of elements in 
'defaults' would imply.

Potential solutions:
 1. Swap posonlyargs and args.
 2. Add a separate pos_defaults list.

--
messages: 347932
nosy: Benjamin.S.Wolf
priority: normal
severity: normal
status: open
title: ast.arguments has confusing args/posonlyargs ordering
type: behavior
versions: Python 3.8

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