Add first and last number of a list

Question

I am asked to add the first and last numbers in a list. This is what I came up with:

def addFirstAndLast(x): 
    return x[0] + x[-1]

But when I run the code, i get an error that says:

IndexError: list index out of range

I can't find the problem though and when I searched for this question, the answers were equal to my code.

Maybe it has to do with the test cases:

1. addFirstAndLast([2])
2. addFirstAndLast([2, 2, 3])
3. addFirstAndLast([])

Can you help me please?

Answer 1

You need to check if your list is empty or not.

def addFirstAndLast(x): 
    return (x[0] + x[-1]) if x else 0

Answer 2

The last test case passes an empty list. An empty list has neither [0] nor [-1] elements.

Answer 3

当然，在您的第3种情况下，没有项目，因此没有相关的索引。

Answer 4

If your list is empty, then you do not have the first and the last elements. Try the following to solve your problem:

def add_first_and_last(x):
    if x:
        return x[0] + x[-1]
    else:
        return 0  # Or whatever you want

You can also try:

def add_first_and_last(x):
    return x[0] + x[-1] if x else 0

Answer 5

In your last case 3. addFirstAndLast([]) isnt there any index at [0] and [-1]

because the list is empty!

So you should make an example if x == []: return x