[typing] `nn.Parameter` return type identified as `Tensor` by `pyright`

[randolf-scholz]

🐛 Describe the bug

Type checking the following script with pyright fails (but not with mypy):

from typing import assert_type, reveal_type
import torch

w = torch.randn(3)
p = torch.nn.Parameter(w)
assert_type(p, torch.nn.Parameter)  # ❌ expected "Parameter" but received "Tensor"
reveal_type(torch.nn.Parameter.__new__)
# (self: type[Self@TensorBase], *args: Unknown, **kwargs: Unknown) -> Tensor

My guess what's happening:

1. TensorBase defines: def __new__(self, *args, **kwargs) -> Tensor: ... in the stub torch/_C/__init__.pyi
2. Parameter.__new__ is untyped. Both pyright and mypy show it's self: type[Self@TensorBase] -> Tensor, so reusing the superclasses type.
3. mypy ignores the discrepancy and treats the result as an nn.Paramter anyway.

It seems the issue can be fixed by simply changing the signature in TensorBase.__new__ to

def __new__(cls, *args, **kwargs) -> Self

Versions

• torch 2.3.0
• pyright 1.1.360