def execute(args):
    """
    Executes the *run* subprogram with parsed commandline *args*.
    """
    task_family = None
    error = None

    # try to infer the task module from the passed task family and import it
    parts = args.task_family.rsplit(".", 1)
    if len(parts) == 2:
        modid, cls_name = parts
        try:
            mod = __import__(modid, globals(), locals(), [cls_name])
            if hasattr(mod, cls_name):
                task_cls = getattr(mod, cls_name)
                if not issubclass(task_cls, Task):
                    abort("object '{}' is not a Task".format(args.task_family))
                task_family = task_cls.task_family
        except ImportError as e:
            logger.warning("import error in module {}: {}".format(modid, e))
            error = e

    # read task info from the index file and import it
    if task_family is None:
        index_file = Config.instance().get_expanded("core", "index_file")
        if os.path.exists(index_file):
            info = read_task_from_index(args.task_family, index_file)
            if not info:
                abort("task family '{}' not found in index".format(args.task_family))
            modid, task_family, _ = info
            __import__(modid, globals(), locals())

    # complain when no task could be found
    if task_family is None:
        if error:
            raise error
        else:
            abort("task '{}' not found".format(args.task_family))

    # import the module and run luigi
    luigi_run([task_family] + sys.argv[3:])
Executes the *run* subprogram with parsed commandline *args*.