[SOLVED] How to force absolute path to be relative when joining?

How to force absolute path to be relative when joining?

What is the idiomatic way to turn an absolute path into a relative path when joining?

Inputs:

abs = r"\\server\share\data"
newroot = r"X:\project"

Desired result:

X:\project\server\share\data

Both os.path.join() and pathlib.Path().joinpath() trim everything after the drive letter:

>>> os.path.join(newroot, abs)
'\\\\server\\share\\data'

>>> pathlib.Path(newroot).joinpath(abs)
WindowsPath('//server/share/data')

I can make them work by stripping the leading slashes:

>>> os.path.join(newroot, abs[2:])
'X:\\project\\server\\share\\data'

but that means I need to wrap in a test to find out whether the incoming path is actually absolute and to count how many slashes to remove. This just feels like a place for me to create bugs.

Note: Windows syntax is shown but I imagine the problem is cross platform and best-practice answer is probably that way also.

Solution

PurePath.relative_to seems to do the job:

>>> Path("/mnt") / (Path("/some/where").relative_to("/"))
PosixPath('/mnt/some/where')