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

Paul Moore p.f.moore at gmail.com
Sat Apr 16 08:05:25 EDT 2016

On 16 April 2016 at 12:21, Stephen J. Turnbull <stephen at xemacs.org> wrote:

OK, you win, fspath needs to be polymorphic.

But you've just shifted me to -1 on "os.fspath": it's an attractive nuisance. EIBTI, applications and high-level library functions should use os.fsdecode or os.fsencode.

I presume your expectation is that os.fsencode/os.fsdecode will work with objects supporting the fspath protocol?

So the question for me is, if I'm writing a function that takes a path argument p (in the most general sense - I want my function to be able to handle anything the stdlib functions can) then how do I write the code? There are 4 cases I can think of:

  1. I just want to pass the argument on to other functions - just do so, stdlib functions will work fine.
  2. I need a string - use os.fsdecode(p)
  3. I need bytes - use os.fsencode(p)
  4. I need a guaranteed pathlib.Path object so that I can use Path methods - convert via pathlib.Path(os.fsdecode(p))

I guess there's the possibility that you want to deliberately reject bytes-like paths, and it's not immediately obvious how you'd do that without os.fspath or using the fspath protocol directly, but I'm not sure what anyone gains by doing so (maybe the chance to fail early? but doesn't using fsdecode mean I never need to fail at all?)

While I don't have any specific reason to object to os.fspath, I'd appreciate someone describing a concrete use case that needs it (and isn't covered by any of the options above).

Paul

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