[Python-Dev] Pathlib enhancements - acceptable inputs and outputs for __fspath__ and os.fspath()

[Random832]

On Mon, Apr 11, 2016, at 13:36, Brett Cannon wrote:
> How about we take something from the "explicit is better than implicit"
> playbook and add a keyword argument to os.fspath() to allow bytes to pass
> through?

Except, we already know how to convert a bytes-path into a str (and vice
versa) with sys.getfilesystemencoding and surrogateescape. So why not
just have the argument specify what return type is desired?

def fspath(path, *, want_bytes=False):
    if isinstance(path, (bytes, str)):
        ppath = path
    else:
        try:
            ppath = path.__fspath__()
        except AttributeError:
            raise TypeError
    if isinstance(ppath, str):
        return ppath.encode(...) if want_bytes else ppath
    elif isinstance(ppath, bytes):
        return ppath if want_bytes else ppath.decode(...)
    else:
        raise TypeError

This way the posix os module can call the function and have the bytes
value already prepared for it to pass to the real open() syscall.

You could even add the same thing in other places, e.g. os.path.join
(defaulting to if the first argument is a bytes).