Tuple slice by variable results in incorrect type

[asottile]

from typing import Tuple

sz = 2
x: Tuple[int, ...] = (1, 2)[:sz]

$ mypy --version
mypy 0.711
$ mypy t.py
mt.py:4: error: Incompatible types in assignment (expression has type "int", variable has type "Tuple[int, ...]")

[asottile]

this is of course reduced from a larger program to a minimal reproduction

[emmatyping]

I checked and you can accomplish this with Literal and Final:

from typing import Tuple
from typing_extensions import Final

sz: Final = 2
x: Tuple[int, ...] = (1, 2)[:sz]

or if you prefer, a Literal[2] annotation should work as well for sz.

[asottile]

in reality, sz is not a literal -- it's used in the following way:

ver = tuple(int(p) for p in x.split('.'))
sz = len(ver)
return min_ver[:sz] <= ver <= max_ver[:sz]

however this is lost when converting to a minimal testcase

Here's the current code with the # type: ignore -- this is definitely a bug and not a question, a slice of a tuple should never return a scalar

[emmatyping]

Ah, you are correct, sorry I misunderstood the issue.

E: also it seems the same does not happen for lists, so this is a bug in tuple handling code.

[emmatyping]

It seems the changes in #3514 made the incorrect decision to return the union of elements when given a slice. I'm working on a fix.

[asottile]

👏👏👏 awesome! thanks for the quick fix on this one 🎉