Description

JelleZijlstra

opened on Jun 16, 2023

Issue body actions

Currently, the constructors for AST nodes accept arbitrary keyword arguments and don't enforce any value:

>>> node=ast.FunctionDef(what="is this")
>>> node.what
'is this'
>>> node.name
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'FunctionDef' object has no attribute 'name'

Problems with the current situation:

• To make a correct AST node, you have to pass every attribute, including ones that could sensibly default to an empty list
• You cannot rely on attributes like name being present
• It's possible to create useless, broken AST nodes like the above
• Introspection tools can't easily tell what the signature of the constructor is supposed to be
• Adding new fields to an AST node causes various compatibility issues (PEP-695: Potentially breaking changes made to __match_args__ attributes of AST nodes #104799)

Proposed solution for 3.13:

• Default all fields to some sensible value if they are not provided to the constructor: an empty list for list fields, and None for other fields.
• Emit a DeprecationWarning if the constructor is passed arguments that it doesn't recognize (e.g., what above). In 3.15, this will raise an error.
• Add a __text_signature__ to the AST classes indicating the expected signature.

Linked PRs

• gh-105858: Improve AST node constructors #105880
• gh-105858: Expose some union-related objects as internal APIs #116025

Reacted by Alex Waygood, Carl Meyer, Tomas R., Oleg Iarygin, chirk and Mikhail Efimov

Activity

1. JelleZijlstra

   added

   type-featureA feature request or enhancementA feature request or enhancement

   topic-parser

   on Jun 16, 2023
2. furkanonder commented on Jun 16, 2023

   

   furkanonder

   on Jun 16, 2023

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   CC: @isidentical
3. JelleZijlstra

   added a commit that references this issue on Jun 17, 2023

   pythongh-105858: Improve AST node constructors

   b1b73d9
4. brandtbucher commented on Jun 20, 2023

   

   brandtbucher

   on Jun 20, 2023

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   Yes please! This has been such a pain point for me.

   One note: we should probably only default optional fields (?) to None, and require everything else.
5. JelleZijlstra commented on Jun 20, 2023

   

   JelleZijlstra

   on Jun 20, 2023

   MemberAuthor

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   One note: we should probably only default optional fields (?) to None, and require everything else.

   Agree, I ended up doing that in my draft PR. Omitting a required field (e.g. FunctionDef.name) will raise a DeprecationWarning, as will passing a bogus field.

   Reacted by Brandt Bucher, Oleg Iarygin and chirk
6. iritkatriel

   added

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on Nov 27, 2023
7. JelleZijlstra

   added a commit that references this issue on Feb 28, 2024

   gh-105858: Improve AST node constructors (#105880)

   ed4dfd8
8. JelleZijlstra commented on Feb 28, 2024

   

   JelleZijlstra

   on Feb 28, 2024

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   Merged!

   Reacted by Alex Waygood
9. JelleZijlstra

   closed this as completedon Feb 28, 2024
10. Privat33r-dev

    added a commit that references this issue on Feb 28, 2024

    pythongh-105858: Improve AST node constructors (python#105880)

    1745629
11. JelleZijlstra commented on Feb 28, 2024

    

    JelleZijlstra

    on Feb 28, 2024

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    Reopening as I broke all the buildbots
12. JelleZijlstra

    reopened this on Feb 28, 2024
13. JelleZijlstra

    added a commit that references this issue on Feb 28, 2024

    pythongh-105858: Expose some union-related objects as internal APIs

    5142722
14. gvanrossum

    added a commit that references this issue on Feb 28, 2024

    pythongh-105858: Improve AST node constructors (python#105880)

    ab5339f
15. encukou

    added a commit that references this issue on Feb 28, 2024

    gh-105858: Expose some union-related objects as internal APIs (GH-116025

    d53560d
16. JelleZijlstra

    closed this as completedon Feb 28, 2024
17. woodruffw

    added 2 commits that reference this issue on Mar 4, 2024

    pythongh-105858: Improve AST node constructors (python#105880)

    7ddc0d8

    pythongh-105858: Expose some union-related objects as internal APIs (p…

    a5fd325
18. adorilson

    added 2 commits that reference this issue on Mar 25, 2024

    pythongh-105858: Improve AST node constructors (python#105880)

    052e900

    pythongh-105858: Expose some union-related objects as internal APIs (p…

    7eb8096
19. hroncok commented on Mar 26, 2024

    

    hroncok

    on Mar 26, 2024

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    There might be a regression: #117266
20. diegorusso

    added 2 commits that reference this issue on Apr 17, 2024

    pythongh-105858: Improve AST node constructors (python#105880)

    3a32841

    pythongh-105858: Expose some union-related objects as internal APIs (p…

    e7f3eda

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