os.Path.join() is used to join two segments of the path adding the platform-dependent separator to the returned path:
CALL os.Path.join(begin, end) RETURNING newpath
where
Typically, this function is called for when there is a need to construct a path with no system-specific code using the correct path separator:
CALL os.Path.join(os.Path.homedir(), file_name) RETURNING newpath