gettext.GNUTranslations.__init__’s argument has an incorrect type

[Jayman2000]

mypy says that this program is wrong:

from gettext import GNUTranslations

with open("foo.mo", mode='rb') as mo_file:
    GNUTranslations(mo_file)

mypy’s output:

main.py:4: error: Argument 1 to "GNUTranslations" has incompatible type "BufferedReader"; expected "Optional[IO[str]]"
Found 1 error in 1 file (checked 1 source file)

I believe that fp (gettext.GNUTranslations.__init__’s argument) should have the type Optional[IO[bytes]], not Optional[IO[str]].

[TeamSpen210]

The problem is that NullTranslations (its base class) is hinted as taking an IO[str] | None, but GNUTranslations needs a binary file. NullTranslations doesn't actually do anything with the file, just store it for subclasses to use so the best solution would probably be to make NullTranslations take IO | None and then constrain in GNUTranslations.

[srittau]

I'd say we just type NullTranslations according to how we type GNUTranslations (as long as it doesn't contradict the actual implementation in the former) as the latter is the only "real" translations class we have. We also should replace IO with a tight protocol.