8000 Local annotation turns local variables in cells · Issue #130924 · python/cpython · GitHub
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markshannon opened this issue Mar 6, 2025 · 3 comments · Fixed by #131843
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Local annotation turns local variables in cells #130924

markshannon opened this issue Mar 6, 2025 · 3 comments · Fixed by #131843
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@JelleZijlstra
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interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error

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@markshannon
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markshannon commented Mar 6, 2025 •
edited by bedevere-app bot
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Bug report

Bug description:

Compiling this function

def f(x):
    a:x
    return x

Gives this bytecode:

  --           MAKE_CELL                0 (x)

   1           RESUME                   0

   3           LOAD_DEREF               0 (x)
               RETURN_VALUE

Local variable annotations are supposed to be ignored by Python (they are used by static type checkers only),
so the addition of the annotation should not change the generated code.
The expected disassembly:

   1           RESUME                   0

   3           LOAD_LAST                0 (x)
               RETURN_VALUE

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs
@markshannon markshannon added the type-bug An unexpected behavior, bug, or error label Mar 6, 2025
@JelleZijlstra JelleZijlstra self-assigned this Mar 6, 2025
@gvanrossum
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Maybe @JelleZijlstra can look into this -- it smells like an unanticipated effect of PEP 749?

@JelleZijlstra
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Yes, I already assigned it to myself to look into.

I think this is harmless in the sense that it doesn't change any behavior we should guarantee, but it's a pessimization.

@picnixz picnixz added the interpreter-core (Objects, Python, Grammar, and Parser dirs) label Mar 7, 2025
@sergey-miryanov
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I can confirm that this is related to PEP-749.
a:x introduces a child scope for __annotate__ and x is a free variable for that scope and this is poisons x for the whole function.

JelleZijlstra added a commit to JelleZijlstra/cpython that referenced this issue Mar 28, 2025
@JelleZijlstra
pythongh-130924: Do not create cells for usages of names in local ann…
989b47f 
…otations
@bedevere-app bedevere-app bot mentioned this issue Mar 28, 2025
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JelleZijlstra added a commit that referenced this issue Mar 29, 2025
@JelleZijlstra
gh-130924: Do not create cells for usages of names in local annotatio…
425f60b 
…ns (#131843)
@sourcery-ai sourcery-ai bot mentioned this issue Mar 30, 2025
Merged
seehwan pushed a commit to seehwan/cpython that referenced this issue Apr 16, 2025
@JelleZijlstra @seehwan80
pythongh-130924: Do not create cells for usages of names in local ann…
7ac1ed0 
…otations (python#131843)
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interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error
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gh-130924: Do not create cells for usages of names in local annotations JelleZijlstra/cpython
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@sergey-miryanov @JelleZijlstra @gvanrossum @markshannon @picnixz
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