Inserting list into another list using loops only:

Question

I'm using the current version of python. I need to return a copy of list1 with list2 inserted at the position indicated by index i.e if the index value is 2, list2 is inserted into list 1 at position 2. I can only use for/while loops, the range function & the list_name.append (value) methods and the lists cannot be sliced. So if list1 list1 = boom list2 = red and the index value = 2, how do I return a new list = boredom? I have this so far:

list1 = ['b','o','o','m']
list2 = ['r','e','d']
index = 2
new_list = []

if index > len(list1):
    new_list = list1 + list2
    print (new_list)
if index <= 0:
    new_list = list2 + list1
    print (new_list)

Answer 1

An alternative approach to Padriac's - using three for loops:

list1 = ['b','o','o','m']
list2 = ['r','e','d']

n = 2
new_list = []
for i in range(n): # append list1 until insert point
    new_list.append(list1[i])
for i in list2: # append all of list2
    new_list.append(i)
for i in range(n, len(list1)): # append the remainder of list1
    new_list.append(list1[i])

Answer 2

Once you hit the index, use an inner loop to append each element from list2:

for ind, ele in enumerate(list1):
    # we are at the index'th element in list1 so start adding all
    # elements from list2
    if ind == index:
        for ele2 in list2:
            new_list.append(ele2)
    # make sure to always append list1 elements too      
    new_list.append(ele)
print(new_list)
['b', 'o', 'r', 'e', 'd', 'o', 'm']

If you must use range just replace enumerate with range:

new_list = []

for ind in range(len(list1)):
    if ind == index:
        for ele2 in list2:
            new_list.append(ele2)
    new_list.append(list1[ind])
print(new_list)
['b', 'o', 'r', 'e', 'd', 'o', 'm']

Or without ifs using extend and remove if allowed:

new_list = []
for i in range(index):
    new_list.append(list1[i])
    list1.remove(list1[i])
new_list.extend(list2)
new_list.extend(list1)

Appending as soon as we hit the index means the elements will be inserted from the correct index, the elements from list1 must always be appended after your if check.