Personally, I like the original wording a bit better because it states what is returned, rather than implying a boolean result via the word "whether", which might be confusing for non-english-native readers.

A quick grep shows that there's a lot of places where we're using Return whether to indicate a boolean return type (though admittedly I may be responsible for quite a few of them, as I also prefer that wording). It's also quite common in the CPython docs (for example).

Can we not clobber file like this, please?

Also, when reassigning a variable within a context like this, I don't think the close() gets called on the new object because the context manager is holding a reference to the original object.

Clobbering what? file is not a builtin (... anymore). And I'd say it's a much nicer variable name than fh...

The fact that the codec writer doesn't get closed doesn't matter (and anyways it will get closed by the GC), what matters is that the file itself gets closed.

import codecs
import contextlib


class filelike:  # mocks file
    def close(self):
        print("closed")


@contextlib.contextmanager
def cm():  # mocks open_file_cm
    print("enter")
    f = filelike()
    yield f
    f.close()
    print("exit")


with cm() as file:
    file = codecs.getwriter("utf-8")(file)


print("done")

prints

enter
closed
exit
done

so the file is indeed closed before the contextmanager is exited.

It would be nice to give the default rcParams setting:
https://matplotlib.org/devdocs/devel/documenting_mpl.html?highlight=documenting#rcparams

done