Description

lgeiger

opened on May 19, 2026

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Currently the AST doesn't allow frozendict as constants when compiled:

import ast
node = ast.Expression(body=ast.Constant(value=frozendict({"a": 1})))
compile(ast.fix_missing_locations(node), "<string>", "eval")

Traceback (most recent call last):
  File "<python-input-0>", line 4, in <module>
    compile(ast.fix_missing_locations(node), "<string>", "eval")
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: got an invalid type in Constant: frozendict

This is implemented for frozenset

node = ast.Expression(body=ast.Constant(value=frozenset({"a", "b"})))
compile(ast.fix_missing_locations(node), "<string>", "eval")

<code object <module> at 0x1067203b0, file "<string>", line 1>

so it makes sense to do the same for frozendict.

Linked PRs

• gh-150045: Add frozendict support to the compiler and AST constants #150050

Activity

1. JelleZijlstra commented on May 19, 2026

   

   JelleZijlstra

   on May 19, 2026

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   Can you clarify what you need? This already works:

   >>> import ast
   >>> ast.Constant(frozendict({"a": 1, "b": 1}))
   ... 
   Constant(value=frozendict({'a': 1, 'b': 1}), kind=None)
   >>> ast.unparse(_)
   "frozendict({'a': 1, 'b': 1})"
   

   And I see no special casing for frozenset in the AST module.

   Reacted by Lukas Geiger

   Reacted by Lukas Geiger
2. lgeiger commented on May 19, 2026

   

   lgeiger

   on May 19, 2026

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   @JelleZijlstra sorry for the incomplete issue. I hit cmd-enter accidentally but you where faster than I could fix it 🚀.

   Indeed defining a frozendict constant works. However it fails when compiling:

   import ast
   node = ast.Expression(body=ast.Constant(value=frozendict({"a": 1})))
   compile(ast.fix_missing_locations(node), "<string>", "eval")

   I updated the issue comment. I am happy to submit a PR to fix this. I think I have it mostly working.
3. aisk

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on May 19, 2026
4. StanFromIreland

   added

   interpreter-core(Objects, Python, Grammar, and Parser dirs)(Objects, Python, Grammar, and Parser dirs)

   on May 19, 2026
5. methane commented on May 19, 2026

   

   methane

   on May 19, 2026

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   In the case of frozenset, we use frozenset to optimize code like if x in {"spam", "ham", "egg"}.

   But would this kind of optimization really be useful for frozendict?
   Or is there some other reason for frozendict to be supported by the AST?

   I am opposed to adding features that are not used just for the sake of symmetry with frozenset.

   Reacted by Jelle Zijlstra, Peter Bierma, Bénédikt Tran, Kirill Podoprigora and Bartosz Sławecki
6. picnixz

   added

   pendingThe issue will be closed if no feedback is providedThe issue will be closed if no feedback is provided

   on May 19, 2026
7. serhiy-storchaka

   added this to Inspect issues 🔍on Jul 3, 2026
8. lgeiger commented on Aug 19, 2026

   

   lgeiger

   on Aug 19, 2026

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   I had another look at this, and indeed the additional optimisations are not really useful. I didn't realise that CPython itself won't actually create frozendicts as ast constants on its own which indeed doesn't make this a very useful optimisation. 37d8189 might still be useful in the future if having the ability to compile a frozendict ast constant similar to frozenset is desired. Closing this issue for now. Sorry about the noise.
9. lgeiger

   closed this as completedon Aug 19, 2026
10. github-project-automation

    moved this to Done in Inspect issues 🔍on Aug 19, 2026
11. StanFromIreland

    closed this as not plannedon Aug 19, 2026

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