def get_difference(one, two):
    """Compute the differences between two blocks."""
    if len(one) != len(two):
        raise Exception("blocks are of different dimensions")
    
    diffs = []
    for y in range(len(one)):
        line1 = one[y]
        line2 = two[y]
        if len(line1) != len(line2):
            raise Exception("blocks are of different dimensions")
        
        for x in range(len(line1)):
            c1 = line1[x]
            c2 = line2[x]
            
            if c1 != c2:
                diffs.append((x, y, c2))
    return diffs