[Python-Dev] file system path protocol PEP

[Brett Cannon]

On Thu, 12 May 2016 at 11:36 Guido van Rossum <guido at python.org> wrote:

> On Thu, May 12, 2016 at 10:18 AM, Brett Cannon <brett at python.org> wrote:
>
>> On Thu, 12 May 2016 at 09:25 Guido van Rossum <guido at python.org> wrote:
>>
> def fspath(p: Union[str, bytes, PathLike]) -> Union[str, bytes]:
>>>     if isinstance(p, (str, bytes)):
>>>         return p
>>>     try:
>>>         return p.__fspath__
>>>     except AttributeError:
>>>         raise TypeError(...)
>>>
>>
>>> Other than that I think the PEP is already in fine shape.
>>>
>>
>> - Bytes: I strongly believe that os.fspath() should be a thin wrapper
>> around the __fspath__ protocol, like next() wraps the .__next__ protocol.
>> It should not get into bytes vs. string politics. If your app really needs
>> strings, call os.fsdecode(). So this is my version (unoptimized):
>>
>> Just to double-check, did you mean for __fspath__ to only be an attribute
>> in your example, or did you leave off the `()` by accident? As of right now
>> the PEP is proposing a method for the protocol to follow common practice of
>> using methods and in case the representation is not always pre-computed and
>> thus not necessarily giving the wrong impression that the attribute access
>> is cheap. But admittedly an attribute was previously proposed and there
>> wasn't a terribly strong argument against it beyond "we historically
>> haven't done it that way", so I'm open to swapping to an attribute if
>> that's your preference.
>>
>>>
> Whoops. Didn't mean to change that! Yes, __fspath__ should remain a
> method. You can breathe again. :-)
>

That's a mechanical change so not exactly the most stressful aspect of this
PEP. :) I'll add the attribute angle to the Rejected Ideas, though.

Anyway, with your strong preference of how to tweak os.fspath() what
specifically would you like to see discussed at this point? Assuming the
os.fspath() -> bytes discussion is dealt with, the only open issues listed
in the PEP are the naming and placement of the ABC and how to do type hints
for all of this (thanks to the dichotomy of path objects using the protocol
and path-like objects which is the union of path object, str, and bytes and
the joy of trying to name all of this well).
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