Description

corona10

opened on Mar 24, 2026

Issue body actions

This idea came up during a conversation with @Fidget-Spinner.

dct = frozendict(a=1)
def foo():
    dct['a'] # fold this to 1

When a frozendict is a promoted constant in the JIT, subscript lookups like dct['a'] should be foldable to the constant value at compile time. This would make frozendict lookups and match/case on frozendict significantly faster. If implemented, this optimization could create strong motivation for users to adopt frozendict in many more places, anywhere a dict is used as a read only lookup table, configuration mapping, or dispatch table.

Plan to start from REPLACE_OPCODE_IF_EVALUATES_PURE in optimizer_bytecodes.c and extend it to handle _BINARY_OP_SUBSCR_DICT for frozendict constant

cc @vstinner

Linked PRs

• gh-146381: Fold frozendict(key=const, ...) calls to LOAD_CONST #146423
• gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPCODE_IF_EVALUATES_PURE #146490
• gh-146381: Constant fold local frozendict subscript lookups via recording #146564

Activity

1. corona10

   self-assigned this

   on Mar 24, 2026
2. corona10

   added

   topic-JIT

   performancePerformance or resource usagePerformance or resource usage

   on Mar 24, 2026
3. StanFromIreland

   added

   type-featureA feature request or enhancementA feature request or enhancement

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

   on Mar 24, 2026
4. corona10

   added 6 commits that reference this issue on Mar 25, 2026

   pythongh-146381: Fold frozendict(key=const, ...) calls to LOAD_CONST

   a09aef5

   pythongh-146381: Fold frozendict subscript via _BINARY_OP_SUBSCR_FROZ…

   77ad3d4

   pythongh-146381: Fold frozendict subscript via _BINARY_OP_SUBSCR_FROZ…

   098ac8b

   gh-146381: Constant-fold frozendict subscript lookups via REPLACE_OPC…

   5992238

   pythongh-146381: Constant fold local frozendict subscript lookups via…

   fc38b65

   pythongh-146381: Constant fold local frozendict subscript lookups via…

   170a3e0
5. corona10 commented on Apr 4, 2026

   

   corona10

   on Apr 4, 2026

   MemberAuthor

   More actions

   Anyway global frozendict now become optimized.
6. corona10

   closed this as completedon Apr 4, 2026
7. clin1234

   added a commit that references this issue on Apr 16, 2026

   pythongh-146381: Constant-fold frozendict subscript lookups via REPLA…

   708b5dd
8. ljfp

   added a commit that references this issue on Apr 25, 2026

   pythongh-146381: Constant-fold frozendict subscript lookups via REPLA…

   9f6238c

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