def _get_challenger_module(challenger_name):
    """
    Return given challenger's module, importing it as necessary.
    """
    try:
        imported_module = __import__('tiddlyweb.web.challengers.%s' %
            challenger_name, {}, {}, ['Challenger'])
    except ImportError:
        imported_module = __import__(challenger_name, {}, {}, ['Challenger'])
    return imported_module.Challenger()
