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

[Ethan Furman]

On 04/11/2016 01:42 PM, Victor Stinner wrote:
> 2016-04-11 21:00 GMT+02:00 Brett Cannon:

>> I'm -0 on allowing __fspath__ to return bytes, but we can see what others
>> think.
>
> With the PEP 383, a bytes filename can be stored as str using the
> surrogateescape error handler. So DirEntry can convert a bytes path to
> str using os.fsdecode().

I am far from a unicode expert, but if I understand this correctly you 
are proposing that DirEntry.__whatever__ can always return a str using 
the surogateescape (SE) method.

However, before this SE string can be used, it would need to be 
converted back to bytes, and with the same SE method, yes?  And this has 
already been implemented in the stdlib?

So my concern in such a case is what happens if we pass this SE string 
somewhere else: a UTF-8 file, or over a socket, or into a database? 
Does this have issues that we wouldn't face if we just used bytes?

--
~Ethan~