iter(...) is not revealed the same as __iter__ method
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Description
Bug Report
We are having issues with the pandas-stubs repo where the inference for __iter__ is different with iter(...).
With __iter__ we are seeing the right inference while with iter(...)
To Reproduce
from typing import Any, Generic, Never, TypeVar, reveal_type
_T_EXPANDING = TypeVar("_T_EXPANDING")
_T_STR = TypeVar("_T_STR", bound=Series)
class StringMethods(Generic[_T_EXPANDING, _T_STR]):
def __getitem__(self, key: int) -> _T_STR: ...
def __iter__(self) -> Never: ...
class Series:
@property
def str(self) -> StringMethods[Any, Series]: ...
def _0() -> None:
reveal_type(StringMethods().__iter__()) # all 4 type checkers give Never
def _1() -> None:
reveal_type(iter(Series().str)) # mypy: Any, pyright, pyrefly: Never, ty: Unknown
Expected Behavior
It is identifying it as Any.
Actual Behavior
We expect Never.
Your Environment
- Mypy version used: mypy 1.19.1 (compiled: yes)
- Mypy command-line flags: mypy test_file.py
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.14
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the provided Python reproducer with mypy 1.19.1 and compare reveal_type(StringMethods().iter()) with reveal_type(iter(Series().str)). Trace the handling of the iter(...) expression relative to the iter method; done means mypy reports Never for the iter(...) case without changing the expected behavior elsewhere.
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
- Clearly specified
- Newbie friendliness
- 48/100