• Register
Welcome to Kodlogs, programming questions and answer website.
0 votes
What does IndexError list index out of range mean? What is index error in Python?

How do you remove an item from a list in Python?  I am a new programmer and i need suggestions for this asap. Thanks
by (1.4k points)  
reshown by

1 Answer

0 votes

How to go about list index out of range errors in Python so I would be discussing what you can do in terms of debugging technique how you can find out where is the problem and what is the problem in the code and how you can go about solving it so let's look at one of the code that I have here which gives list index out of range err so the first hint that we would want to go get is from the trace backup cells so here it says line number five has list index out of range so that basically means we are trying to access an element in the list which is whose index is beyond the beyond the last index in the list so the only place where we are accessing any element over here in line 5 is this this thing so basically it indicates that element must be what is causing the error so what we could do in a very in a very basic sense is put out a print statement just before this line printing out element and lantus initial list to see what is the problem I don't know what the code is doing or it's trying to do but this is how I would go about debugging it know if I print it out I see that elements value is 5 while the lists length is also 5 and if you know the basics of array then you know if the length of the list is 5 then your index ranges from 0 to 4 so if your element itself is 5 that means you're trying to access something that is not there in the list so that's why you're getting this list index out of range now the way we would solve this problem is to understand what it is trying to do algorithmically and then resolve the basic cause of the issue so here what we are trying to do is from an initial list we are trying to build a square list which is basically the square of each of the element so now here if you see in line number 4 we are trying to loop over the elements of the list and then we are trying to access the value at an index which is equal to element but element itself is not the index so what we should be doing instead of we should be looping over the indexes in the initial list and then access the element and that index and then raise it to the power of two this is one of the ways we could do it or if he wants to loop over the elements itself what we would need to do is we would just need to do element ^ power to raise to the power of two and that should give us the spur see here you can see that this fix the code let's try to look at another code and try to debug that so here we see the line number three is causing the issue and it says that list index is out of range so again very nicely if it open the code and just before we are trying to access this we would print out I and Delano I don't know else sorry and just run the code so here we see the initially eyes value 0 then it is 1 then it is true then it is 3 in the notice for so you know that the length of L if we open the code we see little L has 5 elements and we do a for loop over the indexes so I would range from 0 to 4 with just a case over here that we can see that I is ranging from 0 to 4 but as you can see the length of the list is decreasing so basically in this code we are doing some operation we are trying to modify the list so the pop operation basically changes the length of the list so if you remember from Python basics if you pop out an element it would reduce the length by one and it would remove that element from the list so what is happening over here is your length of the list is decreasing and you are ranging you are looping from zero to four but the length has reduced to three so now you are at an index four but the length is three so you're trying to access an element which does not exist in the list anymore so how do you go about fixing the situation first of all even the reason it happens is because when you do a for loop it initializes the values of I initially it doesn't do it each time like in a wild loop so the way I would fix it basically would be to change a for loop with a while loop so what I would do is I would initialize I to zero and while I is less than this if this is while I is less than length of L this and then I would increment I towards the end and then I think they're missing the print statement so what we are want to do is what this code was trying to do initially as it was trying to remove all trees from the list now again if we see we are doing the same thing but in the while loop each time your condition is evaluated it would work with a new length unlike the for loop where the I values were initialized at the beginning and it was not checking the length again and again as it was changing so now if we run the code we see that it gives out the list with three as remote as we wanted it to so these are the basic ideas about how to go about debugging list index out of range first is to look at the stock trace and try to identify where in the code you're trying to access an element which is out of range and then do a couple of print statements around the line to see what is the value of that index and what is the actual length of the list and this would give you an indication there is something wrong with logic with the algorithm in your code and that is how you would go about debugging this less than the X out of range .

by (9.8k points)