Paul Ganssle <p.gans...@gmail.com> added the comment:
I am not seeing any compelling reasons to avoid supporting negative indexes
*or* slices here.
If I had to guess about the confusing semantics of negative indices, I would
guess it's the fact that the index in the -1 position for a non-empty Path will
always be `Path('.')`. Since that's not terribly useful, it might be reasonable
to have negative indices start counting at `len(p)-2`.
That said, I don't think this is a big deal, and I think we have more
speculation on why this was avoided in the first place than we have actual
objections to changing it, so I vote for changing it.
I think our best option is to say that the semantics of indexing `.parents`
should be the same as indexing the result of casting it to a tuple, so this
should be true:
p = Path(x)
assert p.parents[y] == tuple(p.parents)[y]
For all values of `x` and `y`.
I've gone ahead and changed the version support matrix to 3.10 only, since I
think that this was a deliberate choice and we should be considering this an
enhancement rather than a bugfix. That said, I'll admit that it's on the
borderline — the semantics of sequences are unambiguous (see, which says that
sequences support both slices and negative indices:
https://docs.python.org/3/library/stdtypes.html#typesseq ), and PEP 428
explicitly says that .parents returns a "an immutable sequence of the path's
logical ancestors":
https://www.python.org/dev/peps/pep-0428/#sequence-like-access . So if someone
is motivated to try and make the case that this is a bugfix that could be
backported to earlier supported versions, I won't stand in their way.
----------
nosy: +p-ganssle
versions: -Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9
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