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

Ethan Furman ethan at stoneleaf.us
Sun Apr 10 12:16:39 EDT 2016

On 04/09/2016 10:31 PM, Nick Coghlan wrote:

On 10 April 2016 at 02:41, Ethan Furman wrote:

When somebody hands you bytes rather than text you need to worry about the encoding, and you need to worry about returning bytes rather than text yourself. https://hg.python.org/cpython/rev/e44410e5928e#l4.1 provides an illustration of how fiddly that can get, and that's in the URL context - cross-platform filesystem path handling is worse, since you need to worry about the significant differences between the way Windows and *nix handle binary paths, and you can't use os.sep directly any more (since that's always text).

Okay, that makes sense.

DirEntry can still get the check, it can just throw TypeError when it represents a binary path (that's one of the advantages of using a method-based protocol - exceptions on method calls are more acceptable than exceptions on property access).

I guess I don't see the point of this. Either DirEntry's [1] only get partial support (which is only marginally better than the no support pathlib currently has), or stdlib code will need to catch those errors and then do an isinstance check to see if knows what the type is and how to deal with it [1].

On the other hand, if fspath is allowed to hold bytes then the algorithm gets easier:

As a practicality argument that seems a lot easier for everybody.

-- Ethan

[1] Being a low-level function I think working with either bytes or str is entirely appropriate for DirEntry.

[2] DirEntry? Oh yeah, grab the .path attribute. Something else? Bah, let the exception propogate.

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