scipy-stubs: `scipy.optimize.least_squares` function inferred as module

As reported in https://github.com/scipy/scipy-stubs/issues/939, mypy seems to infer scipy.optimize.least_squares as a ModuleType. Other type-checkers (pyright, basedpyright, pyrefly) correctly infer it as a function.

from typing import reveal_type
from scipy.optimize import least_squares

reveal_type(least_squares)

• mypy: Revealed type is "types.ModuleType"
• pyrefly: revealed type: (fun: (🍝) -> OptimizeResult
• (based)pyright: Type of "least_squares" is "(fun: (🍝) -> OptimizeResult"

(🍝 = the huge function signature)

This seems to occur on (at least) scipy-stubs 1.16.2.0 and 1.16.2.3, using mypy 1.18.2.

To repro, install scipy-stubs[scipy]==1.16.2.3 (currently the latest) from pypi or scipy-typed from conda.

Here's are the relevant bits of code:

1. optimize/__init__.pyi re-exports from ._lsq import least_squares through __all__
2. optimize/_lsq/__init__.pyi re-exports from .least_squares import least_squares through __all__
3. optimize/_lsq/least_squares.pyi contains the definition for the least_squares function

It looks like mypy ignores step optimize/_lsq/__init__.pyi from 2., causing it to resolve the optimize._lsq.least_squares module, instead of (explicitly re-exported) optimize._lsq.least_squares.least_squares function.

I expect to be able to work around this by changing from ._lsq import least_squares in optimize/__init__.pyi to from ._lsq.least_squares import least_squares.

Riproduci il report con scipy-stubs[scipy]==1.16.2.3 e mypy 1.18.2, utilizzando l’esempio di reveal_type. Confronta optimize/init.pyi, optimize/_lsq/init.pyi e optimize/_lsq/least_squares.pyi, quindi verifica che l’importazione di scipy.optimize.least_squares riveli la funzione invece di ModuleType.