[Python-Dev] pathlib - current status of discussions

Michael Mysinger cybersol at yahoo.com
Thu Apr 14 03:03:00 EDT 2016

Brett Cannon <brett <at> python.org> writes:

> https://gist.github.com/brettcannon/b3719f54715787d54a206bc011869aa1 has 
the four potential approaches implemented (although it doesn't follow the 
"separate functions" approach some are proposing and instead goes with the 
allow_bytes approach I originally proposed). 

Thanks Brett, it is definitely a start! Maybe I am just more unimaginative 
than most, but since interoperability is the goal, I would ideally be able 
to play with a full implementation where all the stdlib functions Nick 
originally mentioned accepted these "rich path" objects. 

However, for concrete example purposes, maybe it is sufficient to start with 
your fspath function, a toy RichPath class implementing __fspath__, and 
something like os.path.join, which is a meaty enough example to test some of 
the functionality. I posted a gist of a string only example at 

After playing with and considering the 4 possibilities, anything where 
__fspath__ can return bytes seems like insanity that flies in the face of 
everything Python 3 is trying to accomplish. 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? So for me 
that eliminates #3 and #4.

Also the version #2 accepting bytes in os.fspath felt like it could be a 
very minor convenience, but even the str only version #1 is just requires 
one isinstance check in the rare case you need to also deal with bytes (see 
the os.path.join example in the gist above). So I lean toward the str only 
#1 version. 

In any case I would start with the strict str only full implementation and 
loosen it either in 3.6 or 3.7 depending on what people think after actually 
using it.

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