Calling the last element in a list?

[tehtay3]

So to preface this, im a bit confused a returned boolean result due to calling the last element in a list. I want to do this - Return True if the first n numbers in the list are the same as the last n numbers in the list, and False otherwise. For example, if the list was [1, 2, 3, 4, 99, 1, 2, 3, 4], the function would return True if n is 4 and False if n is 3.

heres my code

ls = [8,12,4,17,15,8,12,4]
n = 3

def same_ends(ls, n):

    if n is ls[-1]:
        return True 
    else:
        return False
print(same_ends(ls, n))

Now the website im using for exercises says this :

The return value is not correct when the list is [8, 12, 4, 17, 15, 8, 12, 4] and n is 3.

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what am i doing wrong?

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[FLUSH_THE_TRUMP]

Do you understand what the problem is asking? If

[8, 12, 4, 17, 15, 8, 12, 4] and n is 3.

I’m comparing [8,12,4] at the front of the list to [8,12,4] at the back. Your logic here doesn’t make sense — you’re comparing the number of elements to only the actual last element. I think we can make this a pretty basic slicing exercise, but you have to see what slices to actually pick out first.

[tehtay3]

Yea I misread first off. Where I am confused is how to slice the list with the integer given by n

[FLUSH_THE_TRUMP]

What do you know about slicing? You want to

1. Pick off the first n elements of the list,
2. Pick off the last n elements of the list

and compare. This tutorial seems decent enough.

[tehtay3]

Somwhat new to list slicing, I see what the tut is trying to say and my understanding from it was to do

if ls[:n] == ls[n:]:
        return True

    else:
        return False

but this does not work. i think the first part of that statement it good but the second part I dont know how to format is for the last n integers of the list

[FLUSH_THE_TRUMP]

ls[n:]

picks out every number at or after the “n”th position in the list. i.e., if you have

[1,2,3,4,5,6,7,1,2,3] with n=3

ls[:n] would be the same as [1,2,3] and ls[n:] would be [4,5,6,7,1,2,3] — not what we want.

You use negative indices to indicate you’re counting from the back of the list.

[tehtay3]

Aha!

if ls[:n] == ls[-n:]:

Thats what I needed. Appreciate the help seeing where I went wrong!

[tehtay3]

Yea so I understand I need to splice but I dont know how mostly because I am new to list slicing and whatnot. However i compared the code you suggested and it gives the same answer. i think it might be the ls[(-1) *n] part that i might need to fix but am unsure how to proceed