[Python-ideas] tweaking the file system path protocol

[Serhiy Storchaka]

23.05.17 20:04, Brett Cannon пише:
> On Tue, 23 May 2017 at 03:13 Wolfgang Maier 
> <wolfgang.maier at biologie.uni-freiburg.de 
> <mailto:wolfgang.maier at biologie.uni-freiburg.de>> wrote:
>     My proposal is to change this to:
>     1) check whether the type of the argument is str or bytes *exactly*; if
>     so, return the argument unchanged
>     2) check wether __fspath__ can be called on the type and returns an
>     instance of str, bytes, or any subclass (just like in the current
>     version)
>     3) check whether the type is a subclass of str or bytes and, if so,
>     return it unchanged
> 
> What exactly is the performance issue you are having that is leading to 
> this proposal?

It seems to me that the purpose of this proposition is not performance, 
but the possibility to use __fspath__ in str or bytes subclasses. 
Currently defining __fspath__ in str or bytes subclasses doesn't have 
any effect.

I don't know a reasonable use case for this feature. The __fspath__ 
method of str or bytes subclasses returning something not equivalent to 
self looks confusing to me.