sys.exit() is not considered as noreturn

[socketpair]

https://mypy-play.net/?mypy=latest&python=3.10&flags=strict%2Cstrict-equality&gist=e86aa52c05acd36b6c04067cb6f44ce1

import sys

def main() -> int:
    return sys.exit(42)

MyPy finds nothing wrong here.

Anyway, this should be valid:

try:
    sys.exit(42)
except SystemExit:
    print('xxx') # this line IS reachable.

i.e. this function either raises specific exception or noreturn.

[JelleZijlstra]

Can you clarify what you think the bug is? Mypy is correct when it doesn't produce any errors on your first sample, because a function that never returns is a valid Callable[[], int].

[sobolevn]

Looks like sys.exit is indeed recognised as returning NoReturn: https://mypy-play.net/?mypy=latest&python=3.10&flags=strict%2Cstrict-equality%2Cwarn-unreachable&gist=ef39ea5ba16960f2dd4274349a2c142d

So, it looks fine to me!

[socketpair]

Using return value of noreturn function is an error, indeed.

[sobolevn]

Feel free to reopen if you have other questions / problems :)

[socketpair]

@sobolevn please reopen. It's not fixed actually.

[sobolevn]

Can you please specify what example is not fixed?

[socketpair]

The first one. Mypy does not see any errors in using value of noreturn function.

[erictraut]

The first code sample is not a bug. Mypy is correct in not emitting an error here. NoReturn (which is equivalent to the recently-introduced typing.Never type) is a bottom type in the Python type system, and it is is compatible with all other types. A return value of type NoReturn is compatible with the declared return type int.

[socketpair]

I think, Noreturn must not be compatible with any other type. What the case when it should be compatible ?

[socketpair]

Should be def sys.exit(arg: int) -> Never. Does not it ? That is the same as -> NoReturn here. Both must be incompatible with any other type, like int.