Python: replace an item in a list with a list of items

Question

in a python program I have a list that I would like to modify:

a = [1,2,3,4,5,1,2,3,1,4,5]

Say every time I see 1 in the list, I would like to replace it with 10, 9, 8. My goal is to get:

a = [10,9,8,2,3,4,5,10,9,8,2,3,10,9,8,4,5]

What's a good way to program this? Currently I have to do a 'replace' and two 'inserts' every time I see a 1 in the list.

Thank you!

Answer 1

If you want to do everything in place, then you could try do something like this:

while i < len(a):
    if a[i] == 1:
        a[i : i + 1] = [10, 9, 8]
    i += 1

But IMHO it would be better to build a new list from scratch rather than modifying the existing one in place.

Answer 2

This probably isn't very efficient but it's fun to one-line things:

[item for sublist in [[x] if x != 1 else [10, 9, 8] for x in a] for item in sublist]

Answer 3

Create a new list, with values replaced:

b = []
for z in a:
    b.extend([10, 9, 8] if z == 1 else [z])

Answer 4

Just a normal list comprehension would do the job

>>> [y for x in a for y in ([10,9,8] if x==1 else [x])]
[10, 9, 8, 2, 3, 4, 5, 10, 9, 8, 2, 3, 10, 9, 8, 4, 5]