Interoperability with other path libraries (PEP 519)

[levic]

Python 3.6 introduced PEP 519

Short summary in python 3.6 here: https://docs.python.org/3/whatsnew/3.6.html#pep-519-adding-a-file-system-path-protocol

import unipath
import pathlib

print(unipath.Path('a', 'b', pathlib.Path('c', 'd')))

Presently the above code would fail with TypeError: arguments must be str, unicode, list, int, long, or Path

If os.fspath is present it could be used to convert a path-like object into a string.

(unipath.Path could also be changed to implement __fspath__ but since str is already an ancestor class I'm not sure that what it would achieve)

[levic]

(Note that pathlib.Path('a', 'b', unipath.Path('c', 'd')) already works because str is an ancestor of unipath.Path)

[levic]

@mikeorr Given that you've stated Unipath is in maintenance mode, would you accept a patch if I implemented this?

[mikeorr]

Yes, that's a good idea. I've read about .fspath but it never occurred to me that this related to Unipath. I'm still transitioning from Python 2 to 3 and I'm waiting until I'm fully on Python 3.6 before using 'pathlib' where the stdlib functions support it because it's too much to manage a Python 2/3 codebase at the same time as a must-str()-pathlib codebase: it cancels out most of the benefits of using 'pathlib' in the first place.

Also if you have any ideas for #23 that would be helpful. I have no idea what's wrong or what to do about it.