NamedTuple Subclass Thinking It Returns a Tuple

[Py-mon]

Environment data

• Language Server version: v2024.6.1
• OS and version: Windows 11
• Python version (& distribution if applicable, e.g. Anaconda): 3.11

Code Snippet

from typing import NamedTuple


class Vector(NamedTuple("Vector", [("y", int), ("x", int)])):
    def __add__(self, vector: tuple[int, int]):
        cls = type(self)
        vector = super().__new__(cls, *vector)
        return type(self)(self.y + vector.y, self.x + vector.x)


print(Vector(1, 2) + (3, 1))

Expected behavior

When hovering over vector, it is the type Vector

Actual behavior

When hovering over vector, it is the type tuple[int, int]

Logs

2024-06-25 19:40:40.068 [info] Send text to terminal: �
2024-06-25 19:40:40.277 [info] Send text to terminal: cls
2024-06-25 19:40:40.277 [info] Send text to terminal:  c:; cd 'c:\Users\jacob\OneDrive\Documents\Programming\Python\Pyframe'; & 'c:\Users\jacob\AppData\Local\Programs\Python\Python311\python.exe' 'c:\Users\jacob\.vscode\extensions\ms-python.debugpy-2024.6.0-win32-x64\bundled\libs\debugpy\adapter/../..\debugpy\launcher' '55472' '--' 'C:\Users\jacob\OneDrive\Documents\Programming\Python\Pyframe\rep.py' 

[debonte]

@Py-mon, sorry for the long delay on this.

When hovering over vector, it is the type tuple[int, int]

This is by design, since you've annotated the vector parameter as tuple[int, int]. If I'm misunderstanding the issue here, please let me know.

def __add__(self, vector: tuple[int, int]):

[Py-mon]

@debonte The type of vector changes.
vector = super().__new__(cls, *vector)

[debonte]

I see. I agree that's weird. I'm not super familiar with NamedTuple, but it seems like Vector is a subtype of tuple[int, int] given that Pyright considers the assignment legal. So I'm not sure why the type of vector isn't narrowed there.

Transferring to Pyright.

[erictraut]

Yes, the type of vector should be narrowed on assignment in this case. Pyright wasn't handling this narrowing case correctly because the narrowed type is a type variable (Self) rather than a concrete type.

This will be fixed in the next release of pyright.

[erictraut]

This is addressed in pyright 1.1.384