def reverse_complement(seq):
    """Takes the reverse-complement of DNA seq
    
    Args:
        seq (str)
    Returns:
        seq (str): reverse complemented
    Raises:
        ValueError: if input sequence is None or empty str
    """
    if not seq:
        raise ValueError("input sequences mut be non-empty string")

    return seq[::-1].translate(str.maketrans("ACGTN", "TGCAN"))