PurePath

This module offers classes representing filesystem paths with semantics appropriate for different operating systems. Path classes are divided between pure paths, which provide purely computational operations without I/O, and concrete paths, which inherit from pure paths but also provide I/O operations.

という事で、今回のPurePathはPathをつくるだけの関数のようです。

PurePath("/hoge","bar/buzz")
# PurePosixPath('/hoge/bar/buzz')

賢いので、"."であれば無視してくれます

PurePath("hoge",".","bar/buzz")
# PurePosixPath('hoge/bar/buzz')

11.1. pathlib — Object-oriented filesystem paths — Python 3.6.4 documentation