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Add support for frozendict as AST Constant #150045
Description
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.
Activity
JelleZijlstra commentedon May 19, 2026
Can you clarify what you need? This already works:
And I see no special casing for
frozensetin the AST module.lgeiger commentedon May 19, 2026
@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:
I updated the issue comment. I am happy to submit a PR to fix this. I think I have it mostly working.
methane commentedon May 19, 2026
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.
lgeiger commentedon Aug 19, 2026
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.