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[Python-Dev] file system path protocol PEP

Koos Zevenhoven k7hoven at gmail.com
Sun May 15 07:57:39 EDT 2016 
On Fri, May 13, 2016 at 7:43 PM, Chris Angelico <rosuav at gmail.com> wrote:
[...]
> "Check" accepts subclasses; "CheckExact" doesn't (it's like "type(x)
> is str"). The question is, which one SHOULD be being done?

Indeed it should do "Check", so that path libraries that do inherit
from str will still work (see also below).

> What should this do:
>
> class TmpPath(str):
>     def __fspath__(self):
>         return "/tmp/"+self
> x = TmpPath("foo/bar")
> open(x, "w")
>
> Does that respect __fspath__, or respect the fact that it's a string?

It should not respect __fspath__ because that would mean the behavior
is different in older versions of Python(!). This also means that such
code should never be written (except for that example you wrote ;-).
So indeed, composition would be the way to go.

So yes, I still think str subclasses should not implement __fspath__,
and that, at the very least, the docs should say that :).

-- Koos


> ChrisA
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