import threading


def concurrent_map(func, data):
    """
    Similar to the bultin function map(). But spawn a thread for each argument
    and apply `func` concurrently.

    Note: unlike map(), we cannot take an iterable argument. `data` should be an
    indexable sequence.
    """

    N = len(data)
    result = [None] * N

    # wrapper to dispose the result in the right slot
    def task_wrapper(i):
        result[i] = func(data[i])

    threads = [threading.Thread(target=task_wrapper, args=(i,)) for i in range(N)]
    for t in threads:
        t.start()
    for t in threads:
        t.join()

    return result