[issue39897] `pathlib.Path.is_mount()` calls `Path(self.parent)` and therefore misbehaves in `Path` subclasses

[Barney Gale]

Change by Barney Gale <barney.gale at gmail.com>:


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keywords: +patch
pull_requests: +18196
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/18839

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue39897>
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