# Python: Lists - Double Index HELP! SOS!

#1

I really need help understanding this exercise. I am completely lost to what is happening in the syntax. I’ve done well up until this point. I need someone to explain to what is happening in this code from start to bottom and thoroughly.

This is the solution to the portal, however I don’t get what is happening after the if statement.

1. What is happening when we use lst[index] as a variable?
2. Why are we using the index inside of which are meant for list (if I am correct)?

I DON’T KNOW I’M JUST SUPER CONFUSED!!!
HELP!!!

def double_index(lst, index):
if index < len(lst):
lst[index] = lst[index] * 2
return lst

#Uncomment the line below when your function is done
print(double_index([3, 8, -10, 12], 2))

Lists - Double Index

#2

It is not a variable so much as a reference to the `index` of the list `lst` that is passed to the function. The element at that index is then multiplied by two and stored at the same index.

When print the returned list, it will be,

``````[3, 8, -20, 12]
``````

Notice that the third value in the list (index[2]) is now -20 from the previous -10.

``````lst[index]
``````

The square brackets `[ ]` are known as the subscript. It is how we access the element (value) at position `index` in the list, `lst`.

#3

You’re awesome, Thank you very much for that in-depth explanation. I understand much better now.