PermissionError: [Errno 13] Permission denied

This happens if you are trying to open a file, but your path is a folder.

This can happen easily by mistake.

To defend against that, use:

import os

path = r"my/path/to/file.txt"
assert os.path.isfile(path)
with open(path, "r") as f:
    pass

The assertion will fail if the path is actually of a folder.