Why do I get List index out of range when trying to add consecutive numbers in a list using for i in list

Question

Given the following list

a = [0, 1, 2, 3]

I want to create a new list b, which consists of elements for which the current and next values of a are summed. It will contain 1 less element than a.

Like this:

b = [1, 3, 5]

Here's what I've tried:

b = []

for i in a:

    b.append(a[i + 1] + a[i])

The trouble is I keep getting this error:

IndexError: list index out of range

Can somone help me with this?

Answer 1

The problem in your for loop is that:

• In your for loop, you're iterating through the elements of a list a. You used the items in the list to index in the body of the loop. fix this issue by iterating over a range of indexes instead:    

     for i in range(len(a))

• The next issue is that if you're indexing not only a[i] but also a[i+1], you'll get an IndexError. To fix that, you should subtract 1 from len(a) in order to get a range sequence 0 1 2 3. Since you're using an index i+1, you'll still get the last element, but this way you will avoid the error.

I hope this helps you.