Python - insert element at specific index without using insert function

Question

just a heads up. My code probably is way off. I'm new and i'm trying my best to figure it out but i'm struggling

So far i have this:

def insert_value(my_list, value, insert_position):

    new_list = []
    for i in range(len(my_list)):
        if i == insert_position:
            new_list.append(value)
            i += 1

            return new_list

this is the code calling my function:

str_list3 = ['one','three','four', 'five', 'six']
new_list = list_function.insert_value(str_list3, 'two', 1)
print(new_list)
str_list4 = ['i', 't']
str_list4 = list_function.insert_value(str_list4, 'p', 0)
print(str_list4)
str_list4 = list_function.insert_value(str_list4, 's', -1)
print(str_list4)
str_list4 = list_function.insert_value(str_list4, 's', 7)
print(str_list4)

and:

num_list2 = [1, 3, 4, 5, 6]
num_list2 = list_function.insert_value(num_list2, 2, 1)
print(num_list2)

Am i far off in my solution? I really want to understand where i'm going wrong

Output is meant to be:

['one', 'two', 'three', 'four', 'five', 'six']
['p', 'i', 't']
['s', 'p', 'i', 't']
['s', 'p', 'i', 't', 's']

and:

[1, 2, 3, 4, 5, 6]]

my output is:

['two']
['p']
None

this is all i get

Answer 1

You are actually extremely close, you just need to add some boundary checks:

def insert_value(my_list, value, insert_position):
    if insert_position < 0:
        insert_position = 0
    elif insert_position >= len(my_list):
        insert_position = len(my_list)
    
    new_list = []
    for i in range(len(my_list)):
        if i == insert_position:
            new_list.append(value)
        new_list.append(my_list[i])
    
    if len(my_list) == insert_position:
        new_list.append(value)
    
    return new_list
    
str_list3 = ['one', 'three', 'four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)
str_list4 = ['i', 't']
str_list4 = insert_value(str_list4, 'p', 0)
print(str_list4)
str_list4 = insert_value(str_list4, 's', -1)
print(str_list4)
str_list4 = insert_value(str_list4, 's', 7)
print(str_list4)

num_list2 = [1, 3, 4, 5, 6]
num_list2 = insert_value(num_list2, 2, 1)
print(num_list2)

Output:

['one', 'two', 'three', 'four', 'five', 'six']
['p', 'i', 't']
['s', 'p', 'i', 't']
['s', 'p', 'i', 't', 's']
[1, 2, 3, 4, 5, 6]

Answer 2

You're pretty close except that you've neglected to insert the lines from the original list and you return inside the loop instead of after its done. Also, there is no need to increment i . Its reassigned on the next loop with the next value from range . Basically, range takes the place of the increment.

def insert_value(my_list, value, insert_position):
    new_list = []
    for i in range(len(my_list)):
        if i == insert_position:
            new_list.append(value)
        new_list.append(my_list[i])
    return new_list

str_list3 = ['one','three','four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)

Instead of range you could use enumerate which counts but also gives you the lines iterated, so you don't have to index the array again.

def insert_value(my_list, value, insert_position):
    new_list = []
    for i,v in enumerate(my_list):
        if i == insert_position:
            new_list.append(value)
        new_list.append(v)
    return new_list
    
str_list3 = ['one','three','four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)

Answer 3

You already have a few response on this question. Here is another option to consider:

def insert_value(my_list, value, insert_position):
    if insert_position < 0:
        insert_position = (-insert_position) - 1

    #if you want any negative value to result in position 0
    #then your insert_position assignment will be
    #if insert_position < 0: insert_position = 0
    #the rest of the code will remain the same

    my_list.insert(insert_position,value)

    return my_list

str_list3 = ['one','three','four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)
str_list4 = ['i', 't']
str_list4 = insert_value(str_list4, 'p', 0)
print(str_list4)
str_list4 = insert_value(str_list4, 's', -1)
print(str_list4)
str_list4 = insert_value(str_list4, 's', 7)
print(str_list4)

num_list2 = [1, 3, 4, 5, 6]
num_list2 = insert_value(num_list2, 2, 1)
print(num_list2)

The output for these will be:

['one', 'two', 'three', 'four', 'five', 'six']
['p', 'i', 't']
['s', 'p', 'i', 't']
['s', 'p', 'i', 't', 's']
[1, 2, 3, 4, 5, 6]

Answer 4

#custom function for insert

insert_value =lambda a,value,idx: a[:idx] + [value] + a[idx:]

example

str_list3 = ['one','three','four', 'five', 'six']
new_list = insert_value(str_list3, 'two', 1)
print(new_list)
str_list4 = ['i', 't']
str_list4 = insert_value(str_list4, 'p', 0)
print(str_list4)
str_list4 = insert_value(str_list4, 's', -1)
print(str_list4)
str_list4 = insert_value(str_list4, 's', 7)
print(str_list4)

num_list2 = [1, 3, 4, 5, 6]
num_list2 = insert_value(num_list2, 2, 1)
print(num_list2)

The output for these will be:

['one', 'two', 'three', 'four', 'five', 'six']
['p', 'i', 't']
['s', 'p', 'i', 't']
['s', 'p', 'i', 't', 's']
[1, 2, 3, 4, 5, 6]

Answer 5

Another example but source list will change if need you can copy it

Syntax: lst[index:index] = [obj]

Here is without custom function

str_list = ['one','three','four', 'five', 'six']
str_list[1:1]=['two']
print(str_list)

str_list1=['i', 't']
str_list1[0:0]='p'
print(str_list1)
str_list1[-1:-1]=['s']
print(str_list1)
str_list1[7:7]=['s']
print(str_list1)

num_list2 = [1, 3, 4, 5, 6]
num_list2[1:1]=[2]
print(num_list2)

The output for these will be:

['one', 'two', 'three', 'four', 'five', 'six']
['p', 'i', 't']
['s', 'p', 'i', 't']
['s', 'p', 'i', 't', 's']
[1, 2, 3, 4, 5, 6]