a = [3, 6, 9, 2, 6, 8, 9, 1, 7, 21, 7, 12]

for i in range(1, len(a)):
    t = a[i];
    index = i;
    for j in range(i -1, -1, -1):

        if a[j] > t:
            a[j + 1] = a[j]
            index = j
        else:
            break

    if index != i:
        a[index] = t;

print(a)