def sfx(uri: str) -> str:
    """
    Add a separator to a uri if none exists.

    Note: This should only be used with module id's -- it is not uncommon to use partial prefixes,
    e.g. PREFIX bfo: http://purl.obolibrary.org/obo/BFO_
    :param uri: uri to be suffixed
    :return: URI with suffix
    """
    return str(uri) + ('' if uri.endswith(('/', '#', '_', ':')) else '/')