def to_subject_paths(paths):
if paths is None: return []<EOL>if pimms.is_str(paths): paths = paths.split('<STR_LIT::>')<EOL>paths = [os.path.expanduser(p) for p in paths]<EOL>return [p for p in paths if os.path.isdir(p)]<EOL>
to_subject_paths(paths) accepts either a string that is a :-separated list of directories or a
  list of directories and yields a list of all the existing directories.