Indexing tuple with `slice` object results in wrong type

[rshin]

Example:

x = (1, 2, 3)
y = x[1:3]
z = x[slice(1, 3)]
reveal_locals()

Output from mypy:

note: Revealed local types are:
note:     x: Tuple[builtins.int, builtins.int, builtins.int]
note:     y: Tuple[builtins.int, builtins.int]
note:     z: builtins.int

I believe z should also have type Tuple[builtins.int, builtins.int], or at a minimum Tuple[builtins.int, ...].

[ilevkivskyi]

Yeah, looks like a bug.

[gvanrossum]

It may not be so easy to fix -- what if we write x[slice(a, b)] where all we know is that a and b are ints? The slice class is a simple object defined in typeshed. What's the real world use case?

[JelleZijlstra]

Still reproduces, despite typeshed's overload at https://github.com/python/typeshed/blob/b7d129f727bccb9976940a8db23f06a4c7dccc00/stdlib/builtins.pyi#L794. I guess it's because tuple.__getitem__ for fixed-length tuples is handled specially in mypy and doesn't use the stubs.

[sg495]

Just a note in passing that this is still an issue with mypy 1.7.1 on Python 3.12.