def METHOD_NAME(arg): # -> tuple[int, int]:
    """ Find a user ID and group ID from a string like 'user:group'.  Returns
        a tuple (uid, gid).  If the string only contains a user like 'user'
        then (uid, -1) will be returned.  Raises ValueError if either
        the user or group can't be resolved to valid IDs on the system. """
    ...