Annotate `is_bearable` to return TypeGuard

Looks like TypeGuard is suitable as a return type for is_bearable for it to support mypy. I haven’t tested. Maybe it does support mypy already?

[leycec]

Resolved by db2b98e. Thanks so much for the gentle reminder. I’d gradually forgotten about PEP 647 and typing.TypeGuard, because it’s only supported only Python ≥ 3.10. But have no fear! Python can do anything that it probably shouldn’t, so we forcibly made this work by transparently falling back to bool under Python < 3.10. Dynamically interpreted languages for the win.

Unrelatedly, it turns out our ANSI stripping routine was indeed busted. I’m unclear why exactly that blew up tonight – but it did, spectacularly. But have no fear! I forcibly made that work too by removing a single excessive backslash. If you’re curious, here’s the working version (…which now resides in beartype._util.text.utiltextcolour, just because):

def strip_text_ansi(text: str) -> str:
    # Glory be to the one liner that you are about to read.
    return sub(r'\033[^m]*m', '', text)

\o/

[rsokl]

“Type checkers are special cased to always know what typing_extensions is even if it isn’t installed (it’s treated like part of the standard library)[^1]”. The following should work:

if typing.TYPE_CHECKING:
    from typing_extensions import TypeGuard
else:
    try:
        from typing import TypeGuard
    except ImportError:
        try:
            from typing_extensions import TypeGuard
        except ImportError:
            TypeGuard = bool

This should simplify the code considerably I believe 😄 !

[^1]: A quote from a mypy core dev