[Python-Dev] Defining a path protocol (original) (raw)

Koos Zevenhoven k7hoven at gmail.com
Fri Apr 8 19:05:41 EDT 2016

On Sat, Apr 9, 2016 at 12:53 AM, Brett Cannon <brett at python.org> wrote:

On Fri, 8 Apr 2016 at 14:23 Koos Zevenhoven <k7hoven at gmail.com> wrote:

At this point no one wants to touch bytes paths. If you need that level of control because of multiple encodings within a single file system then you will probably have to stick with managing bytes paths on your own to get the encoding right.

What does this mean? I assume you don't mean os.path.* would stop dealing with bytes? And if not, then you seem to mean that os.fspath would do nothing except call .fspath(). In that case, I think we should go back to it being an attribute (or property) and a variation of the now very famous idiom getattr(path, 'fspath', path) and perhaps have os.fspath do exactly that.

And just because DirEntry supports bytes doesn't mean that any magic method it gains has to carry that forward (it can always raise a TypeError if necessary).

No, but what if some code gets pathnames from whatever other places and passes them on to os.scandir. Whenever it happens to get a bytes path, a TypeError gets raised, but only when it picks one of the DirEntry objects and for instance tries to open(...) it. Of course, I'm not sure how common this is.

It really depends on how we choose to structure the function in terms of just doing the right thing for objects that follow the protocol or if we want to introduce some required structure for the resulting path and implement some type guarantees so you have a better idea of what you will be working with after calling the function.

Do you have an example of potential 'required structure'?

Then the options are either to return Union[str, bytes] or to always return str. And if the latter does not cause any problems, I like it way better, and it seems others would do too. You don't have to convert byte paths to str, you can simply raise an exception in the face of them.

I thought the point was for existing APIs to start supporting path objects, wouldn't raising an exception break the API?

-Koos

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