def intersperse(lis, value):
    """Put value between each existing item in list.

    Parameters
    ----------
    lis : list
        List to intersperse.
    value : object
        Value to insert.

    Returns
    -------
    list
        interspersed list
    """
    out = [value] * (len(lis) * 2 - 1)
    out[0::2] = lis
    return out
Put value between each existing item in list.

    Parameters
    ----------
    lis : list
        List to intersperse.
    value : object
        Value to insert.

    Returns
    -------
    list
        interspersed list