Lots of examples on SO for inserting the same single value into another list at n positions, but can't find anything demonstrating the following:

Take the following lists:

list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] 
list2 = ['this', 'that', 'the', 'other']

Insert each value of list2 into list1 every 2 positions to return:

['a', 'b', 'this', 'c', 'd', 'that', 'e', 'f', 'the', 'g', 'h', 'other']

Alternatively just create a 3rd list with same result.

insert can be used to insert a single value to the list

Let's see what the documentation says about insert:

list.insert(i, x)

Insert an item at a given position. The first
argument is the index of the element before which to insert, so
a.insert(0, x) inserts at the front of the list, and a.insert(len(a),
x) is equivalent to a.append(x).

Inserts before the given index. Let's have a look at an example implementation keeping that in mind:

def ins_n(lst1, lst2, n): # insert every n elements
 indx1 = n
 indx2 = 0
 while(indx1 <= len(lst1)):
 lst1.insert(indx1, lst2[indx2])
 indx1 += 1 + n # add `1` because we insert before the given index
 indx2 += 1
 return lst1

Test it with your example lists and 2:

list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] 
list2 = ['this', 'that', 'the', 'other']

print(ins_n(list1, list2, 2))

Output:

['a', 'b', 'this', 'c', 'd', 'that', 'e', 'f', 'the', 'g', 'h', 'other']

You can use zip with a list comprehension and chunk list1 via this recipe:

from itertools import chain

def chunks(L, n):
 """Yield successive n-sized chunks from L."""
 for i in range(0, len(L), n):
 yield L[i:i + n]

list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] 
list2 = ['this', 'that', 'the', 'other']

zipper = zip(chunks(list1, 2), list2)
res = list(chain.from_iterable((x, y, z) for (x, y), z in zipper))

['a', 'b', 'this', 'c', 'd', 'that', 'e', 'f', 'the', 'g', 'h', 'other']

You can try following solution, simple and clean:

list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] 
list2 = ['this', 'that', 'the', 'other']

i=2
j=0
while(j<len(list1) and j<len(list2)):
 list1.insert(i, list2[j])
 i=i+3
 j=j+1

print(list1)

you can try the following code:

def insert_list(old_list, new_list, n):
 for i, val in enumerate(new_list):
 old_list.insert(n+i*3, val)
 return old_list

Test:

list1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'] 
list2 = ['this', 'that', 'the', 'other']
print(insert_list(list1, list2, 2))

Output:

['a', 'b', 'this', 'c', 'd', 'that', 'e', 'f', 'the', 'g', 'h', 'other']