def cake_decoration(orders):
    """
    IMPORTANT: You should only use list comprehension for this question.
    Follow the syntax guidelines in the writeup.

    Take a list of orders and count the unique letters needed to
    be decorated for orders of even length.

    >>> cake_decoration(['Marina', 'Ruixuan','George'])
    [5, 5]
    >>> cake_decoration([])
    []
    >>> cake_decoration([''])
    [0]
    >>> cake_decoration(["Looooool","Yesssss", 'uncopyrightable.'])
    [3, 16]
    """
    return [len(set(x)) for x in orders if len(x) % 2 == 0 ]