python / python/mypy

Should a method name shadow outer names when quoted or with PEP563?

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bug topic-quoted-annotations topic-runtime-semantics
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Python
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Description

Bug Report

If a class defines a method with a name shadowing outer name, mypy always rejects it in annotations.

To Reproduce

Consider the following snippet (playground):

#from __future__ import annotations

from typing import get_type_hints, get_origin

class Foo:
    def list(self) -> None: ...
    
    def method(self) -> list[str]:  # E: Function "__main__.Foo.list" is not valid as a type  [valid-type]
        return [""]

Foo().method().append("")  # E: "list?[builtins.str]" has no attribute "append"  [attr-defined]

if get_origin(get_type_hints(Foo.method)['return']) is list:
    print("Resolved to builtins.list")
else:
    print("Resolved as something else")

When run against it, mypy is producing a correct valid-type error, matching runtime behaviour.

$ mypy a.py
a.py:8: error: Function "a.Foo.list" is not valid as a type  [valid-type]
a.py:8: note: Perhaps you need "Callable[...]" or a callback protocol?
a.py:11: error: "list?[builtins.str]" has no attribute "append"  [attr-defined]
Found 2 errors in 1 file (checked 1 source file)

$ pyright a.py
/tmp/tmp.StzhaQlnmA/a.py
  /tmp/tmp.StzhaQlnmA/a.py:8:25 - error: Expected class but received "(self: Self@Foo) -> None" (reportGeneralTypeIssues)
1 error, 0 warnings, 0 informations 

$ python a.py
Traceback (most recent call last):
  File "/tmp/tmp.StzhaQlnmA/a.py", line 5, in <module>
    class Foo:
    ...<3 lines>...
            return [""]
  File "/tmp/tmp.StzhaQlnmA/a.py", line 8, in Foo
    def method(self) -> list[str]:  # E: Function "__main__.Foo.list" is not valid as a type  [valid-type]
                        ~~~~^^^^^
TypeError: 'function' object is not subscriptable

Now let's uncomment the future import or quote list[int] (both behave equivalently).

from __future__ import annotations

from typing import get_type_hints, get_origin

class Foo:
    def list(self) -> None: ...
    
    def method(self) -> list[str]:  # E: Function "__main__.Foo.list" is not valid as a type  [valid-type]
        return [""]

Foo().method().append("")  # E: "list?[builtins.str]" has no attribute "append"  [attr-defined]

if get_origin(get_type_hints(Foo.method)['return']) is list:
    print("Resolved to builtins.list")
else:
    print("Resolved as something else")
$ mypy a.py
a.py:8: error: Function "a.Foo.list" is not valid as a type  [valid-type]
a.py:8: note: Perhaps you need "Callable[...]" or a callback protocol?
a.py:11: error: "list?[builtins.str]" has no attribute "append"  [attr-defined]
Found 2 errors in 1 file (checked 1 source file)

$ pyright a.py
0 errors, 0 warnings, 0 informations 

$ python a.py
Resolved to builtins.list

Runtime resolution also (unsurprisingly, probably) works as intended, so mypy does not model runtime semantics correctly?

Expected Behavior

Snippet with PEP563 enabled should pass mypy check

Actual Behavior

a.py:8: error: Function "a.Foo.list" is not valid as a type  [valid-type]
a.py:8: note: Perhaps you need "Callable[...]" or a callback protocol?
a.py:11: error: "list?[builtins.str]" has no attribute "append"  [attr-defined]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

  • Mypy version used: 1.14.1 and latest master
  • Mypy command-line flags: N/A
  • Mypy configuration options from mypy.ini (and other config files): N/A
  • Python version used: 3.13

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running mypy against the provided reproducer with and without quoted annotations or PEP 563 enabled, comparing the result with runtime resolution and pyright. Trace the annotation name-resolution path for method names shadowing outer names, then add coverage for the demonstrated cases and verify that the expected checks pass.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

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