[New-bugs-announce] [issue47161] pathlib method relative_to doesnt work with // in paths

[Jan Bronicki]

New submission from Jan Bronicki <janbronicki at gmail.com>:

The `//` path should be equivalent to `/`, and in some ways, it does behave like that in pathlib. But in the `relative_to` method on a `Path` object, it does not work
This is causing our CI pipeline to fail. In the documentation here you can see `//` being properly processed:

https://docs.python.org/3/library/pathlib.html


```python
In [10]: x=Path("/Library/Video") ; x.relative_to(Path("/"))
Out[10]: PosixPath('Library/Video')

In [11]: x=Path("//Library/Video") ; x.relative_to(Path("/"))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Input In [11], in <cell line: 1>()
----> 1 x=Path("//Library/Video") ; x.relative_to(Path("/"))

File ~/.pyenv/versions/3.8.13/lib/python3.8/pathlib.py:908, in PurePath.relative_to(self, *other)
    906 if (root or drv) if n == 0 else cf(abs_parts[:n]) != cf(to_abs_parts):
    907     formatted = self._format_parsed_parts(to_drv, to_root, to_parts)
--> 908     raise ValueError("{!r} does not start with {!r}"
    909                      .format(str(self), str(formatted)))
    910 return self._from_parsed_parts('', root if n == 1 else '',
    911                                abs_parts[n:])

ValueError: '//Library/Video' does not start with '/'
```

----------
components: Library (Lib)
messages: 416336
nosy: John15321
priority: normal
severity: normal
status: open
title: pathlib method relative_to doesnt work with // in paths
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue47161>
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