How to break a line in an array

for x in range(antall):
    if x == xx:
        xx = xx + 10
        x = str(x)
        seter.append("\nX " + x)
    else:
        x = str(x)
        seter.append("X " + x)
print(seter)

Output: ['X 0', 'X 1', 'X 2', 'X 3', 'X 4', 'X 5', 'X 6', 'X 7', 'X 8', 'X 9', '\nX 10']