l1 = [6,7,7,8,9]
l2 = [1,1,1]
l3 = l1[:K] + l2 + l1[K:]

>>> n, m, k = 10, 5, 4
>>> L1 = range(20, 20+n)
>>> L2 = range(m)
>>> L1, L2
([20, 21, 22, 23, 24, 25, 26, 27, 28, 29], [0, 1, 2, 3, 4])
>>> L1[k:k] = L2[:]
>>> L1
[20, 21, 22, 23, 0, 1, 2, 3, 4, 24, 25, 26, 27, 28, 29]
>>>