def random_insert_seq(lst, seq):
    insert_locations = sample(range(len(lst) + len(seq)), len(seq))
inserts = dict(zip(insert_locations, seq))
input = iter(lst)
lst[:] = [(inserts[pos] if pos in inserts else next(input)) for pos in
    range(len(lst) + len(seq))]
Python | How to append elements to a list randomly