In short: use with_suffix. For example, Path("foo.txt").with_suffix(".ogg") == Path("foo.ogg").

I recently had a Python pathlib.Path whose extension I wanted to change. For example, I wanted to change Path("foo.txt") to Path("foo.ogg").

I did this by using the with_suffix method. For example:

from pathlib import Path

my_path = Path("/foo/bar.txt")
my_path.with_suffix(".ogg")
# => Path("/foo/bar.ogg")

I hope this post helps the next person who wanted to do this!