def split_rows(array:list, l:int=9) -> list:
    """
    Transforms a 1D list into a list of lists with every list holding l 
    elements. Error is raised if array has a length not divisible by l.
    """
    if len(array) % l != 0:
        raise ValueError("split_rows(): Rows in list have different lengths")
    return [array[i:i+l] for i in range(0, len(array), l)]