How to get relative path given a parent of unknown location with Python’s pathlib?

with pathlib.Path.relative_to we can get relative paths with:

>>> from pathlib import Path
>>> Path("/path/to/foo/bar/thing").relative_to("/path/to/foo")
PosixPath('bar/thing')

But what if i don’t know the exact path of the parent directory (but i do know its name)?

for example:

• Path("/path/to/foo/bar/thing") relative to "foo" => PosixPath('bar/thing')
• Path("/path/to/foo/bar/thing") relative to "to" => PosixPath('foo/bar/thing')
• Path("/another_path/to/foo/bar/thing") relative to "foo" => PosixPath('bar/thing')

how do i get a relative path relative to an arbitrary parent directory like this?

Answer

Given

p = Path("/path/to/foo/bar/thing")
relative_to = 'foo'

do

relative_p = Path(*p.parts[p.parts.index(relative_to) + 1:])

Essentially, we grab the parts of the path, find the index of relative_to and slice those parts using that index. Then we pass the sliced parts back to the Path() constructor to get back our relative path.

Another option

import os
relative_p = Path(str(p).split(f'{os.sep}{relative_to}{os.sep}', maxsplit=1)[-1])