def intersperse(lst, item):
    """ Insert item between each item in lst.

    Copied under CC-BY-SA from stackoverflow at:

    https://stackoverflow.com/questions/5920643/
    add-an-item-between-each-item-already-in-the-list

    """
    result = [item] * (len(lst) * 2 - 1)
    result[0::2] = lst
    return result