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annotationlib: ref.evaluate() not working for generics as local variables #138151
Description
Bug report
Bug description:
Usually, when a local variable is introduced after getting a ForwardRef, evaluate() picks this up and correctly evaluates it using the self.__cell__ short-circuit. However, this does not work when that local variable is a generic. It does still work for globals.
from annotationlib import Format, get_annotations
def works_global():
class Demo:
x: sequence_a[int]
fwdref = get_annotations(Demo, format=Format.FORWARDREF)['x']
print(f"Global {fwdref!r}")
global sequence_a
sequence_a = list
evaluated = fwdref.evaluate()
print(f"Evaluated {evaluated!r}")
def works_nongeneric():
class Demo:
nonlocal alias # Optional
x: alias
fwdref = get_annotations(Demo, format=Format.FORWARDREF)['x']
print(f"Global {fwdref!r}")
alias = int
evaluated = fwdref.evaluate()
print(f"Evaluated {evaluated!r}")
def fails():
class Demo:
nonlocal sequence_b
x: sequence_b[int]
fwdref = get_annotations(Demo, format=Format.FORWARDREF)['x']
print(f"Local {fwdref!r}")
sequence_b = list
evaluated = fwdref.evaluate() # NameError
print(f"Evaluated {evaluated!r}")
works_global()
works_nongeneric()
fails()CPython versions tested on:
CPython main branch, 3.14
Operating systems tested on:
Linux
Activity
JelleZijlstra commentedon Aug 26, 2025
I wouldn't expect your
fails()to work: you setsequence_bonly in that function's local scope, and that's not the scope the annotation was defined in.dr-carlos commentedon Aug 26, 2025
Thanks, this is a good point, I forgot to consider that when writing up the example.
I've edited the OP with more complete examples, and put the classes inside the function definitions so the scoping should be correct.
JelleZijlstra commentedon Aug 26, 2025
The problem here is that we don't properly preserve a reference to the cell object that was used to create the ForwardRef. This should be done when we create the ForwardRef (i.e., in get_annotations or code called from it), not in ForwardRef.evaluate. We can probably fix this by putting more information in the
__cell__attribute of the ForwardRef.pythongh-138151: Fix annotationlib handling of multiple nonlocals
dr-carlos commentedon Aug 27, 2025
@JelleZijlstra Is #138161 still necessary given the broader fix in #138164 , or should I close it?
JelleZijlstra commentedon Aug 27, 2025
I don't think #138161 is necessary, but someone will need to review #138164.
gh-138151: Fix annotationlib handling of multiple nonlocals (#138164)
pythongh-138151: Fix annotationlib handling of multiple nonlocals (py…
[3.14] gh-138151: Fix annotationlib handling of multiple nonlocals (G…
efimov-mikhail commentedon Nov 3, 2025
I've checked that merged PRs fix this issue on main and 3.14. So I'll close this.
pythongh-138151: Fix annotationlib handling of multiple nonlocals (py…