def list_diff(first_list, second_list):
    """Utility function to calculate list difference (first_list-second_list)

    Parameters
    ----------
    first_list : list
        First list.

    second_list : list
        Second list.

    Returns
    -------
    diff : different elements.

    """
    second_list = set(second_list)
    return [item for item in first_list if item not in second_list]