Fix stdlib subprocess.Popen.returncode typing

[mnixry]

According to the document, the Popen.returncode should be Optional[int]:

The child return code, set by poll() and wait() (and indirectly by communicate()). A None value indicates that the process hasn’t terminated yet.

[srittau]

The problem with this change is that there are situations where the caller knows that the exit code can't be None, see the mypy primer output above. That said, we should at least change the return type to int | Any to cover the None case. Also obligatory link to python/typing#566.

[mnixry]

The problem with this change is that there are situations where the caller knows that the exit code can't be None, see the mypy primer output above.

Thank you for your explanation.

So according to my understanding, using int instead of Optional<int> is a compromised solution to keep compatibility with the existing code?
I just remember that the type was int | None some time ago, this makes the recent change reasonable for me.

[srittau]

So according to my understanding, using int instead of Optional<int> is a compromised solution to keep compatibility with the existing code?

A mixture of compatibility with existing code, but also not requiring authors of new code to have to add assert in places like this, even though a human reader can clearly spot that the value can't be None.

Edit: But int is also clearly wrong, which is why int | Any would be the best we could do at the moment.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉