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[Python-Dev] pathlib - current status of discussions

Michael Mysinger cybersol at yahoo.com
Thu Apr 14 11:59:56 EDT 2016 
Ethan Furman <ethan <at> stoneleaf.us> writes:

> On 04/14/2016 12:03 AM, Michael Mysinger via Python-Dev wrote:
> > In particular, one RichPath
> > class might return bytes and another str, or even worse the same class 
might
> > sometimes return bytes and sometimes str. When will os.path.join blow up 
due
> > to mixing bytes and str and when will it work in those situations?
> 
> What are you asking here?  ...  Meaning allowing os.fspath() 
> and __fspath__ to return either bytes or str will never cause the 
> combination of bytes and str to work.  Said another way: if you are 
> using os.path.join then all the pieces have be str or all the pieces 
> have to be bytes.

I am saying that if os.path.join now accepts RichPath objects, and those 
objects can return either str or bytes, then its much harder to reason about 
when I have all bytes or all strings. In essence, you will force me to pre-
wrap all RichPath objects in either os.fsencode(os.fspath(path)) or 
os.fsdecode(os.fspath(path)), just so I can reason about the type. And if I 
have to always do that wrapping then os.path.join doesn't need to accept 
RichPath objects and call fspath at all.
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