what does indexerror list assignment index out of range mean

How to Fix the “List index out of range” Error in Python

• learn python

At many points in your Python programming career, you’re going to run into the “List index out of range” error while writing your programs. What does this mean, and how do we fix this error? We’ll answer that question in this article.

The short answer is: this error occurs when you’re trying to access an item outside of your list’s range. The long answer, on the other hand, is much more interesting. To get there, we’ll learn a lot about how lists work, how to index things the bad way and the good way, and finally how to solve the above-mentioned error.

This article is aimed at Python beginners who have little experience in programming. Understanding this error early will save you plenty of time down the road. If you’re looking for some learning material, our Python Basics track includes 3 interactive courses bundled together to get you on your feet.

Indexing Python Lists

Lists are one of the most useful data structures in Python. And they come with a whole bunch of useful methods . Other Python data structures include tuples, arrays, dictionaries, and sets, but we won’t go into their details here. For hands-on experience with these structures, we have a Python Data Structures in Practice course which is suitable for beginners.

A list can be created as follows:

Instead of using square brackets ([]) to define your list, you can also use the list() built-in function.

There are already a few interesting things to note about the above example. First, you can store any data type in a list, such as an integer, string, floating-point number, or even another list. Second, the elements don’t have to be unique: the integer 1 appears twice in the above example.

The elements in a list are indexed starting from 0. Therefore, to access the first element, do the following:

Our list contains 6 elements, which you can get using the len() built-in function. To access the last element of the list, you might naively try to do the following:

This is equivalent to print(x[len(x)]) . Since list indexing starts from 0, the last element has index len(x)–1 . When we try to access the index len(x) , we are outside the range of the list and get the error. A more robust way to get the final element of the list looks like this:

While this works, it’s not the most pythonic way. A better method exploits a nice feature of lists – namely, that they can be indexed from the end of the list by using a negative number as the index. The final element can be printed as follows:

The second last element can be accessed with the index -2, and so on. This means using the index -6 will get back to the first element. Taking it one step further:

Notice this asymmetry. The first error was trying to access the element after the last with the index 6, and the second error was trying to access the element before the first with the index -7. This is due to forward indexing starting at 0 (the start of the list), and backwards indexing starting at -1 (the end of the list). This is shown graphically below:

Looping Through Lists

Whenever you’re working with lists, you’ll need to know about loops. A loop allows you to iterate through all the elements in a list.

The first type of loop we’ll take a look at is the while loop. You have to be a little more careful with while loops, because a small mistake will make them run forever, requiring you to force the program to quit. Once again, let’s try to naively loop through our list:

In this example we define our index, i , to start from zero. After every iteration of our while loop, we print the list element and then go to the next index with the += assignment operator. (This is a neat little trick, which is like doing i=i+1 .)

By the way, if you forget the final line, you’ll get an infinite loop.

We encountered the index error for the same reason as in the first section – the final element has index len(x)-1 . Just modify the condition of the while statement to reflect this, and it will work without problems.

Most of your looping will be done with a for loop, which we’ll now turn our attention to. A better method to loop through the elements in our list without the risk of running into the index error is to take advantage of the range() built-in function. This takes three arguments, of which only the stop argument is required. Try the following:

The combination of the range() and len() built-in functions takes care of worrying about when to stop indexing our list to avoid the index out of range error entirely. This method, however, is only useful if you care about knowing what the index is.

For example, maybe you want to print out the index and the element. In that case, all you need to do is modify the print() statement to print(i, x[i]) . Try doing this for yourself to see the result. Alternatively, you can use The enumerate() function in Python.

If you just want to get the element, there’s a simpler way that’s much more intuitive and readable. Just loop through the elements of the list directly:

If the user inputs an index outside the range of the list (e.g. 6), they’ll run into the list index error again. We can modify the function to check the input value with an if statement:

Doing this prevents our program from crashing if the index is out of range. You can even use a negative index in the above function.

There are other ways to do error handling in Python that will help you avoid errors like “list index out of range”. For example, you could implement a try-exceptaa block instead of the if-else statement.

To see a try-except block in action, let’s handle a potential index error in the get_value() function we wrote above. Preventing the error looks like this:

As you can probably see, the second method is a little more concise and readable. It’s also less error-prone than explicitly checking the input index with an if-else statement.

Master the “List index out of range” Error in Python

You should now know what the index out of range error in Python means, why it pops up, and how to prevent it in your Python programs.

A useful way to debug this error and understand how your programs are running is simply to print the index and compare it to the length of your list.

This error could also occur when iterating over other data structures, such as arrays, tuples, or even when iterating through a string. Using strings is a little different from  using lists; if you want to learn the tools to master this topic, consider taking our Working with Strings in Python course. The skills you learnt here should be applicable to many common use cases.

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Python IndexError: List Index Out of Range Error Explained

• November 15, 2021 December 19, 2022

In this tutorial, you’ll learn how all about the Python list index out of range error, including what it is, why it occurs, and how to resolve it.

The IndexError is one of the most common Python runtime errors that you’ll encounter in your programming journey. For the most part, these these errors are quite easy to resolve, once you understand why they occur.

Throughout this tutorial, you’ll learn why the error occurs and walk through some scenarios where you might encounter it. You’ll also learn how to resolve the error in these scenarios .

The Quick Answer:

Table of Contents

What is the Python IndexError?

Let’s take a little bit of time to explore what the Python IndexError is and what it looks like. When you encounter the error, you’ll see an error message displayed as below:

We can break down the text a little bit. We can see here that the message tells us that the index is out of range . This means that we are trying to access an index item in a Python list that is out of range, meaning that an item doesn’t have an index position.

An item that doesn’t have an index position in a Python list, well, doesn’t exist.

In Python, like many other programming languages, a list index begins at position 0 and continues to n-1 , where n is the length of the list (or the number of items in that list).

This causes a fairly common error to occur. Say we are working with a list with 4 items. If we wanted to access the fourth item, you may try to do this by using the index of 4. This, however, would throw the error. This is because the 4 th item actually has the index of 3.

Let’s take a look at a sample list and try to access an item that doesn’t exist:

We can see here that the index error occurs on the last item we try to access.

The simplest solution is to simply not try to access an item that doesn’t exist . But that’s easier said than done. How do we prevent the IndexError from occurring? In the next two sections, you’ll learn how to fix the error from occurring in their most common situations: Python for loops and Python while loops.

Need to check if a key exists in a Python dictionary? Check out this tutorial , which teaches you five different ways of seeing if a key exists in a Python dictionary, including how to return a default value.

Python IndexError with For Loop

You may encounter the Python IndexError while running a Python for loop. This is particularly common when you try to loop over the list using the range() function .

Let’s take a look at the situation where this error would occur:

The way that we can fix this error from occurring is to simply stop the iteration from occurring before the list runs out of items . The way that we can do this is to change our for loop from going to our length + 1, to the list’s length. When we do this, we stop iterating over the list’s indices before the lengths value.

This solves the IndexError since it causes the list to stop iterating at position length - 1 , since our index begins at 0, rather than at 1.

Let’s see how we can change the code to run correctly:

Now that you have an understanding of how to resolve the Python IndexError in a for loop, let’s see how we can resolve the error in a Python while-loop.

Want to learn more about Python for-loops? Check out my in-depth tutorial that takes your from beginner to advanced for-loops user! Want to watch a video instead? Check out my YouTube tutorial here .

Python IndexError with While Loop

You may also encounter the Python IndexError when running a while loop.

For example, it may be tempting to run a while loop to iterate over each index position in a list. You may, for example, write a program that looks like this:

The reason that this program fails is that we iterate over the list one too many times. The reason this is true is that we are using a <= (greater than or equal to sign). Because Python list indices begin at the value 0, their max index is actually equal to the number of items in the list minus 1.

We can resolve this by simply changing the operator a less than symbol, < . This prevents the loop from looping over the index from going out of range.

In the next section, you'll learn a better way to iterate over a Python list to prevent the IndexError .

Want to learn more about Python f-strings? Check out my in-depth tutorial , which includes a step-by-step video to master Python f-strings!

How to Fix the Python IndexError

There are two simple ways in which you can iterate over a Python list to prevent the Python IndexError .

The first is actually a very plain language way of looping over a list. We don't actually need the list index to iterate over a list. We can simply access its items directly.

This directly prevents Python from going beyond the maximum index.

Want to learn how to use the Python zip() function to iterate over two lists? This tutorial teaches you exactly what the zip() function does and shows you some creative ways to use the function.

But what if you need to access the list's index?

If you need to access the list's index and a list item, then a much safer alternative is to use the Python enumerate() function.

When you pass a list into the enumerate() function, an enumerate object is returned. This allows you to access both the index and the item for each item in a list. The function implicitly stops at the maximum index, but allows you to get quite a bit of information.

Let's take a look at how we can use the enumerate() function to prevent the Python IndexError .

We can see here that we the loop stops before the index goes out of range and thereby prevents the Python IndexError .

Check out some other Python tutorials on datagy, including our complete guide to styling Pandas and our comprehensive overview of Pivot Tables in Pandas !

In this tutorial, you learned how to understand the Python IndexError : list item out of range. You learned why the error occurs, including some common scenarios such as for loops and while loops. You learned some better ways of iterating over a Python list, such as by iterating over items implicitly as well as using the Python enumerate() function.

To learn more about the Python IndexError , check out the official documentation here .

Nik Piepenbreier

Nik is the author of datagy.io and has over a decade of experience working with data analytics, data science, and Python. He specializes in teaching developers how to use Python for data science using hands-on tutorials. View Author posts

1 thought on “Python IndexError: List Index Out of Range Error Explained”

from django.contrib import messages from django.shortcuts import render, redirect

from home.forms import RewardModeLForm from item.models import Item from person.models import Person from .models import Reward, YoutubeVideo # Create your views here.

def home(request): my_reward = Reward.objects.all()[:1] # First Div last_person_post = Person.objects.all()[:1] last_item_post = Item.objects.all()[:1] # 2nd Div lost_person = Person.objects.filter(person=”L”).all()[:1] lost_item = Item.objects.filter(category=”L”).all()[:2] # End 2 div

home_found = Person.objects.all()[:3] home_item = Item.objects.all()[:3] videos = YoutubeVideo.objects.all()[:3] context = { ‘my_reward’: my_reward, ‘lost_person’: lost_person, ‘lost_item’: lost_item, ‘home_found’: home_found, ‘home_item’: home_item, ‘videos’: videos, } if last_person_post[0].update > last_item_post[0].update: context[‘last_post’] = last_person_post else: context[‘last_post’] = last_item_post

return render(request, ‘home/home.html’, context)

# Reward Function

def reward(request): if request.method == ‘POST’: form = RewardModeLForm(request.POST or None) if form.is_valid(): instance = form.save(commit=False) instance.user = request.user instance.save() messages.add_message(request, messages.SUCCESS, ‘Reward Updated .’) return redirect(‘home’) else: form = RewardModeLForm() context = { ‘form’: form, } return render(request, ‘home/reward.html’, context) index out of rage

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Python indexerror: list assignment index out of range Solution

An IndexError is nothing to worry about. It’s an error that is raised when you try to access an index that is outside of the size of a list. How do you solve this issue? Where can it be raised?

In this article, we’re going to answer those questions. We will discuss what IndexErrors are and how you can solve the “list assignment index out of range” error. We’ll walk through an example to help you see exactly what causes this error.

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Without further ado, let’s begin!

The Problem: indexerror: list assignment index out of range

When you receive an error message, the first thing you should do is read it. An error message can tell you a lot about the nature of an error.

Our error message is: indexerror: list assignment index out of range.

IndexError tells us that there is a problem with how we are accessing an index . An index is a value inside an iterable object, such as a list or a string.

The message “list assignment index out of range” tells us that we are trying to assign an item to an index that does not exist.

In order to use indexing on a list, you need to initialize the list. If you try to assign an item into a list at an index position that does not exist, this error will be raised.

An Example Scenario

The list assignment error is commonly raised in for and while loops .

We’re going to write a program that adds all the cakes containing the word “Strawberry” into a new array. Let’s start by declaring two variables:

The first variable stores our list of cakes. The second variable is an empty list that will store all of the strawberry cakes. Next, we’re going to write a loop that checks if each value in “cakes” contains the word “Strawberry”.

If a value contains “Strawberry”, it should be added to our new array. Otherwise, nothing will happen. Once our for loop has executed, the “strawberry” array should be printed to the console. Let’s run our code and see what happens:

As we expected, an error has been raised. Now we get to solve it!

The Solution

Our error message tells us the line of code at which our program fails:

The problem with this code is that we are trying to assign a value inside our “strawberry” list to a position that does not exist.

When we create our strawberry array, it has no values. This means that it has no index numbers. The following values do not exist:

We are trying to assign values to these positions in our for loop. Because these positions contain no values, an error is returned.

We can solve this problem in two ways.

Solution with append()

First, we can add an item to the “strawberry” array using append() :

The append() method adds an item to an array and creates an index position for that item. Let’s run our code: [‘Strawberry Tart’, ‘Strawberry Cheesecake’].

Our code works!

Solution with Initializing an Array

Alternatively, we can initialize our array with some values when we declare it. This will create the index positions at which we can store values inside our “strawberry” array.

To initialize an array, you can use this code:

This will create an array with 10 empty values. Our code now looks like this:

Let’s try to run our code:

Our code successfully returns an array with all the strawberry cakes.

This method is best to use when you know exactly how many values you’re going to store in an array.

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Our above code is somewhat inefficient because we have initialized “strawberry” with 10 empty values. There are only a total of three cakes in our “cakes” array that could possibly contain “Strawberry”. In most cases, using the append() method is both more elegant and more efficient.

IndexErrors are raised when you try to use an item at an index value that does not exist. The “indexerror: list assignment index out of range” is raised when you try to assign an item to an index position that does not exist.

To solve this error, you can use append() to add an item to a list. You can also initialize a list before you start inserting values to avoid this error.

Now you’re ready to start solving the list assignment error like a professional Python developer!

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IndexError: list assignment index out of range in Python

Last updated: Apr 8, 2024 Reading time · 9 min

# Table of Contents

• IndexError: list assignment index out of range
• (CSV) IndexError: list index out of range
• sys.argv[1] IndexError: list index out of range
• IndexError: pop index out of range

Make sure to click on the correct subheading depending on your error message.

# IndexError: list assignment index out of range in Python

The Python "IndexError: list assignment index out of range" occurs when we try to assign a value at an index that doesn't exist in the list.

To solve the error, use the append() method to add an item to the end of the list, e.g. my_list.append('b') .

Here is an example of how the error occurs.

The list has a length of 3 . Since indexes in Python are zero-based, the first index in the list is 0 , and the last is 2 .

Trying to assign a value to any positive index outside the range of 0-2 would cause the IndexError .

# Adding an item to the end of the list with append()

If you need to add an item to the end of a list, use the list.append() method instead.

The list.append() method adds an item to the end of the list.

The method returns None as it mutates the original list.

# Changing the value of the element at the last index in the list

If you meant to change the value of the last index in the list, use -1 .

When the index starts with a minus, we start counting backward from the end of the list.

# Declaring a list that contains N elements and updating a certain index

Alternatively, you can declare a list that contains N elements with None values.

The item you specify in the list will be contained N times in the new list the operation returns.

Make sure to wrap the value you want to repeat in a list.

If the list contains a value at the specific index, then you are able to change it.

# Using a try/except statement to handle the error

If you need to handle the error if the specified list index doesn't exist, use a try/except statement.

The list in the example has 3 elements, so its last element has an index of 2 .

We wrapped the assignment in a try/except block, so the IndexError is handled by the except block.

You can also use a pass statement in the except block if you need to ignore the error.

The pass statement does nothing and is used when a statement is required syntactically but the program requires no action.

# Getting the length of a list

If you need to get the length of the list, use the len() function.

The len() function returns the length (the number of items) of an object.

The argument the function takes may be a sequence (a string, tuple, list, range or bytes) or a collection (a dictionary, set, or frozen set).

If you need to check if an index exists before assigning a value, use an if statement.

This means that you can check if the list's length is greater than the index you are trying to assign to.

# Trying to assign a value to an empty list at a specific index

Note that if you try to assign to an empty list at a specific index, you'd always get an IndexError .

You should print the list you are trying to access and its length to make sure the variable stores what you expect.

# Use the extend() method to add multiple items to the end of a list

If you need to add multiple items to the end of a list, use the extend() method.

The list.extend method takes an iterable (such as a list) and extends the list by appending all of the items from the iterable.

The list.extend method returns None as it mutates the original list.

# (CSV) IndexError: list index out of range in Python

The Python CSV "IndexError: list index out of range" occurs when we try to access a list at an index out of range, e.g. an empty row in a CSV file.

To solve the error, check if the row isn't empty before accessing it at an index, or check if the index exists in the list.

Assume we have the following CSV file.

And we are trying to read it as follows.

# Check if the list contains elements before accessing it

One way to solve the error is to check if the list contains any elements before accessing it at an index.

The if statement checks if the list is truthy on each iteration.

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False .
• 0 (zero) of any numeric type
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

# Check if the index you are trying to access exists in the list

Alternatively, you can check whether the specific index you are trying to access exists in the list.

This means that you can check if the list's length is greater than the index you are trying to access.

# Use a try/except statement to handle the error

Alternatively, you can use a try/except block to handle the error.

We try to access the list of the current iteration at index 1 , and if an IndexError is raised, we can handle it in the except block or continue to the next iteration.

# sys.argv [1] IndexError: list index out of range in Python

The sys.argv "IndexError: list index out of range in Python" occurs when we run a Python script without specifying values for the required command line arguments.

To solve the error, provide values for the required arguments, e.g. python main.py first second .

I ran the script with python main.py .

The sys.argv list contains the command line arguments that were passed to the Python script.

# Provide all of the required command line arguments

To solve the error, make sure to provide all of the required command line arguments when running the script, e.g. python main.py first second .

Notice that the first item in the list is always the name of the script.

It is operating system dependent if this is the full pathname or not.

# Check if the sys.argv list contains the index

If you don't have to always specify all of the command line arguments that your script tries to access, use an if statement to check if the sys.argv list contains the index that you are trying to access.

I ran the script as python main.py without providing any command line arguments, so the condition wasn't met and the else block ran.

We tried accessing the list item at index 1 which raised an IndexError exception.

You can handle the error or use the pass keyword in the except block.

# IndexError: pop index out of range in Python

The Python "IndexError: pop index out of range" occurs when we pass an index that doesn't exist in the list to the pop() method.

To solve the error, pass an index that exists to the method or call the pop() method without arguments to remove the last item from the list.

The list has a length of 3 . Since indexes in Python are zero-based, the first item in the list has an index of 0 , and the last an index of 2 .

If you need to remove the last item in the list, call the method without passing it an index.

The list.pop method removes the item at the given position in the list and returns it.

You can also use negative indices to count backward, e.g. my_list.pop(-1) removes the last item of the list, and my_list.pop(-2) removes the second-to-last item.

Alternatively, you can check if an item at the specified index exists before passing it to pop() .

This means that you can check if the list's length is greater than the index you are passing to pop() .

An alternative approach to handle the error is to use a try/except block.

If calling the pop() method with the provided index raises an IndexError , the except block is run, where we can handle the error or use the pass keyword to ignore it.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• IndexError: index 0 is out of bounds for axis 0 with size 0
• IndexError: invalid index to scalar variable in Python
• IndexError: pop from empty list in Python [Solved]
• Replacement index 1 out of range for positional args tuple
• IndexError: too many indices for array in Python [Solved]
• IndexError: tuple index out of range in Python [Solved]

Borislav Hadzhiev

Web Developer

Copyright © 2024 Borislav Hadzhiev

How to fix IndexError: list assignment index out of range in Python

by Nathan Sebhastian

Posted on Apr 05, 2023

Reading time: 2 minutes

When programming with Python, you might encounter the following error:

This error occurs when you attempt to assign a value to a list using an index that doesn’t already exist in the list.

This tutorial will show you an example that causes this error and how to fix it in practice

How to reproduce this error

Suppose you create a list in your code as follows:

Next, you assign a new value at index [2] in the list as follows:

You’ll get this error:

The error occurs because the index number [2] doesn’t exist in the animals list. Index assignment in a list only allows you to change existing items.

Because the list has two items, the index number ranges from 0 to 1. Assigning a value to any other index number will cause this error.

How to fix this error

To resolve this error, you need to use the append() method to add a new element to the list.

For example, to add the ‘bird’ item:

As you can see, now the ‘bird’ value is added to the list successfully.

Adding the value using the append() method increases the list index range, which enables you to modify the item at the new index using the list assignment syntax.

To summarize, use the append() method when you’re adding a new element and increasing the size of the list, and use the list assignment index when you want to change an existing item in the list.

I hope this tutorial is helpful. Until next time! 👋

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List Index Out of Range – Python Error Message Solved

In this article you'll see a few of the reasons that cause the list index out of range Python error.

Besides knowing why this error occurs in the first place, you'll also learn some ways to avoid it.

Let's get started!

How to Create a List in Python

To create a list object in Python, you need to:

• Give the list a name,
• Use the assignment operator, = ,
• and include 0 or more list items inside square brackets, [] . Each list item needs to be separated by a comma.

For example, to create a list of names you would do the following:

The code above created a list called names that has four values: Kelly, Nelly, Jimmy, Lenny .

How to Check the Length of a List in Python

To check the length of a list in Python, use Python's build-in len() method.

len() will return an integer, which will be the number of items stored in the list.

There are four items stored in the list, therefore the length of the list will be four.

How to Access Individual List Items in Python

Each item in a list has its own index number .

Indexing in Python, and most modern programming languages, starts at 0.

This means that the first item in a list has an index of 0, the second item has an index of 1, and so on.

You can use the index number to access the individual item.

To access an item in a list using its index number, first write the name of the list. Then, inside square brackets, include the intiger that corresponds with the item's index number.

Taking the example from earlier, this is how you would access each item inside the list using its index number:

You can also use negative indexing to access items inside lists in Python.

To access the last item, you use the index value of -1. To acces the second to last item, you use the index value of -2.

Here is how you would access each item inside a list using negative indexing:

Why does the Indexerror: list index out of range error occur in Python?

Using an index number that is out of the range of the list.

You'll get the Indexerror: list index out of range error when you try and access an item using a value that is out of the index range of the list and does not exist.

This is quite common when you try to access the last item of a list, or the first one if you're using negative indexing.

Let's go back to the list we've used so far.

Say I want to access the last item, "Lenny", and try to do so by using the following code:

Generally, the index range of a list is 0 to n-1 , with n being the total number of values in the list.

With the total values of the list above being 4 , the index range is 0 to 3 .

Now, let's try to access an item using negative indexing.

Say I want to access the first item in the list, "Kelly", by using negative indexing.

When using negative indexing, the index range of a list is -1 to -n , where -n the total number of items contained in the list.

With the total number of items in the list being 4 , the index range is -1 to -4 .

Using the wrong value in the range() function in a Python for loop

You'll get the Indexerror: list index out of range error when iterating through a list and trying to access an item that doesn't exist.

One common instance where this can occur is when you use the wrong integer in Python's range() function.

The range() function typically takes in one integer number, which indicates where the counting will stop.

For example, range(5) indicates that the counting will start from 0 and end at 4 .

So, by default, the counting starts at position 0 , is incremented by 1 each time, and the number is up to – but not including – the position where the counting will stop.

Let's take the following example:

Here, the list names has four values.

I wanted to loop through the list and print out each value.

When I used range(5) I was telling the Python interpreter to print the values that are at the positions 0 to 4 .

However, there is no item in position 4.

You can see this by first printing out the number of the position and then the value at that position.

You see that at position 0 is "Kelly", at position 1 is "Nelly", at position 2 is "Jimmy" and at position 3 is "Lenny".

When it comes to position four, which was specified with range(5) which indicates positions of 0 to 4 , there is nothing to print out and therefore the interpreter throws an error.

One way to fix this is to lower the integer in range() :

Another way to fix this when using a for loop is to pass the length of the list as an argument to the range() function. You do this by using the len() built-in Python function, as shown in an earlier section:

When passing len() as an argument to range() , make sure that you don't make the following mistake:

After running the code, you'll again get an IndexError: list index out of range error:

Hopefully this article gave you some insight into why the IndexError: list index out of range error occurs and some ways you can avoid it.

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Python List Index Out of Range – How to Fix IndexError

In Python, the IndexError is a common exception that occurs when trying to access an element in a list, tuple, or any other sequence using an index that is outside the valid range of indices for that sequence. List Index Out of Range Occur in Python when an item from a list is tried to be accessed that is outside the range of the list. Before we proceed to fix the error, let’s discuss how indexing work in Python .

What Causes an IndexError in Python

• Accessing Non-Existent Index: When you attempt to access an index of a sequence (such as a list or a string) that is out of range, an Indexerror is raised. Sequences in Python are zero-indexed, which means that the first element’s index is 0, the second element’s index is 1, and so on.
• Empty List: If you try to access an element from an empty list, an Indexerror will be raised since there are no elements in the list to access.

Example: Here our list is 3 and we are printing with size 4 so in this case, it will create a list index out of range.

Similarly, we can also get an Indexerror when using negative indices.

How to Fix IndexError in Python

• Check List Length: It’s important to check if an index is within the valid range of a list before accessing an element. To do so, you can use the function to determine the length of the list and make sure the index falls within the range of 0 to length-1.
• Use Conditional Statements: To handle potential errors, conditional statements like “if” or “else” blocks can be used. For example, an “if” statement can be used to verify if the index is valid before accessing the element. if or try-except blocks to handle the potential IndexError . For instance, you can use a if statement to check if the index is valid before accessing the element.

How to Fix List Index Out of Range in Python

Let’s see some examples that showed how we may solve the error.

• Using Python range()
• Using Python Index()
• Using Try Except Block

Python Fix List Index Out of Range using Range()

The range is used to give a specific range, and the Python range() function returns the sequence of the given number between the given range.

Python Fix List Index Out of Range u sing Index()

Here we are going to create a list and then try to iterate the list using the constant values in for loops.

Reason for the error –  The length of the list is 5 and if we are an iterating list on 6 then it will generate the error.

Solving this error without using Python len() or constant Value: To solve this error we will take the index of the last value of the list and then add one then it will become the exact value of length.

Python Fix List Index Out of Range using Try Except Block

If we expect that an index might be out of range, we can use a try-except block to handle the error gracefully.

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How to Fix – IndexError list assignment index out of range

The IndexError is a common error that occurs in Python when you try to access an index that is out of range for a list. This error can occur when you try to assign a value to an index that does not exist in the list. In this tutorial, we will discuss how to fix the IndexError list assignment index out of range in Python.

Understanding the Error

Before we dive into the solution, let’s first understand what causes the IndexError list assignment index out of range error. This error occurs when you try to assign a value to an index that does not exist in the list. For example, consider the following code:

In the above code, we are trying to assign the value 4 to the index 3 of the my_list list. However, the my_list list only has three elements, so the index 3 does not exist. This results in the IndexError list assignment index out of range error.

Fixing the Error

To fix the IndexError list assignment index out of range error, you need to make sure that the index you are trying to access or assign a value to exists in the list. You can use an if statement to check if the index exists in the list.

Note that Python sequences also allow negative indexing so be mindful of this when checking if an index exists in a list or not. Let’s look at an example.

Note that if you’re sure that the given index is not negative, you can just check if the index lies in the range 0 to the length of the list using index < len(my_list) .

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If your end goal is to add an element to a list, you can instead use the list append() or insert() functions.

The append() method adds an element to the end of the list, so you don’t have to worry about the index. For example:

Here, we added the element 4 to the end of the list and we didn’t need to provide an index.

If you need to add an element to a specific index in the list, you can use the insert() method. The insert() method takes two arguments: the index where you want to insert the element and the element itself.

In this code, we are using the insert() method to insert the value 4 at the index 3 of the my_list list. Since we are inserting the element at a specific index, the IndexError list assignment index out of range error will be avoided.

The IndexError list assignment index out of range error occurs when you try to assign a value to an index that does not exist in the list. To fix this error, you need to make sure that the index you are trying to access or assign a value to exists in the list. You can do this by checking the length of the list. If you want to add values to a list, you can use the append() method to add elements to the end of the list, or the insert() method to insert elements at a specific index.

You might also be interested in –

• Understand and Fix IndexError in Python
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How to Fix Python IndexError: list assignment index out of range

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• How to Fix Python IndexError: list …

Python IndexError: list assignment index out of range

Fix the indexerror: list assignment index out of range in python, fix indexerror: list assignment index out of range using append() function, fix indexerror: list assignment index out of range using insert() function.

In Python, the IndexError: list assignment index out of range is raised when you try to access an index of a list that doesn’t even exist. An index is the location of values inside an iterable such as a string, list, or array.

In this article, we’ll learn how to fix the Index Error list assignment index out-of-range error in Python.

Let’s see an example of the error to understand and solve it.

Code Example:

The reason behind the IndexError: list assignment index out of range in the above code is that we’re trying to access the value at the index 3 , which is not available in list j .

To fix this error, we need to adjust the indexing of iterables in this case list. Let’s say we have two lists, and you want to replace list a with list b .

You cannot assign values to list b because the length of it is 0 , and you are trying to add values at kth index b[k] = I , so it is raising the Index Error. You can fix it using the append() and insert() .

The append() function adds items (values, strings, objects, etc.) at the end of the list. It is helpful because you don’t have to manage the index headache.

The insert() function can directly insert values to the k'th position in the list. It takes two arguments, insert(index, value) .

In addition to the above two solutions, if you want to treat Python lists like normal arrays in other languages, you can pre-defined your list size with None values.

Once you have defined your list with dummy values None , you can use it accordingly.

There could be a few more manual techniques and logic to handle the IndexError: list assignment index out of range in Python. This article overviews the two common list functions that help us handle the Index Error in Python while replacing two lists.

We have also discussed an alternative solution to pre-defined the list and treat it as an array similar to the arrays of other programming languages.

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[Resolve] IndexError: List Assignment Index Out of Range

When does the IndexError: list assignment index out of range appear?

Python throws an IndexError if you try to assign a value to a list index that doesn’t exist, yet. For example, if you execute the expression list[1] = 10 on an empty list , Python throws the IndexError . Simply resolve it by adding elements to your list until the index actually exists.

Here’s the minimal example that throws the IndexError:

If you run this code, you’ll see that Python throws an IndexError :

You can resolve it by adding two “dummy” elements to the list so that the index 1 actually exists in the list:

Now, Python will print the expected output:

Try to fix the IndexError in the following interactive code shell:

Exercise : Can you fix this code?

So what are some other occurrences of the IndexError?

IndexError in For Loop

Frequently, the IndexError happens if you use a for loop to modify some list elements like here:

Again, the result is an IndexError :

You modify a list element at index i that doesn’t exist in the list. Instead, create the list using the list(range(10)) list constructor.

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How to Fix IndexError: List Index Out of Range in Python

Table of Contents

The IndexError: list index out of range error occurs in Python when an item from a list is attempted to be accessed that is outside the index range of the list. The range of a list in Python is [0, n-1], where n is the number of elements in the list.

Python IndexError Example

Here’s an example of a Python IndexError: list index out of range thrown when trying to access an out of range list item:

In the above example, since the list test_list contains 4 elements, its last index is 3. Trying to access an element an index 4 throws an IndexError: list index out of range :

How to Fix IndexError in Python

The Python IndexError: list index out of range can be fixed by making sure any elements accessed in a list are within the index range of the list. This can be done by using the range() function along with the len() function.

The range() function returns a sequence of numbers starting from 0 ending at the integer passed as a parameter. The len() function returns the length of the parameter passed. Using these two methods together allows for safe iteration over the list up to its final element, thus ensuring that you stay within the valid index range and preventing the IndexError.

Here's how to use this approach to fix the error in the earlier example:

The above code runs successfully and produces the correct output as expected:

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IndexError: list index out of range and python

Why does this occur.

We see this error when indexing a list while using a value outside the range of indexes for the list. Today we'll take a look at some of the most common causes of this error, along with how to solve it using some practical examples.

Cause 1: Indexing the Final List Value

This problem frequently occurs when trying to index the end of a list.

Let's say you've got a list of ten values, but you're only interested in getting the final value in the list. We could do this as shown below:

Recall that indexing in Python starts at zero . We're getting this error because we've gone outside the range of the list. Even though the list has a length of ten, its indexes only range from 0-9, making the tenth index out of range.

We can fix the error by altering the index used to return the final list value, shown in the following solution:

Now that the index is within the correct range, the code runs successfully.

An alternative way of returning list values is to use a negative index. See below for an image showing the negative indexes of example_list , followed by a solution that uses a negative index to return the final list value:

Cause 2: Altering List while Looping

Another common cause of this error is modifying a list while looping over it. Generally, you should rarely change a data structure while looping over it.

Let's say you've got a list of colors called colors . You're not a big fan of the color blue, so you'd like to remove all blue values from the list. We can attempt this as shown below:

This error occurs because the del command changes the list length while in the loop.

At the start of the for loop, the length of colors is five, so the range() function generates the list [0, 1, 2, 3, 4] .

Although our list length decreases every time we delete an item, the range list we are looping through will remain the same. We'll eventually run into the index error in the later stages of our for loop since range() will be providing indexes greater than the length of the list.

To avoid editing the list directly while looping over it, we utilize list comprehension .

In just one line of code, we can remove any blue values from colors .

List comprehension works by creating a new list (as denoted by the brackets), then utilizing a for to iterate through all values in the list. The addition of if color != 'blue' communicates to Python that we're only interested in values that aren't blue, storing these in a new list. Once the for loop has finished iterating through all of the list values, we replace the old list.

This index error is triggered when indexing a list using a value outside of its range of indexes. The best way to avoid it is by carefully considering what range of indexes a list might have, taking into account that list indexes start at zero instead of one. As we've discussed, it's also a good idea to avoid editing a list while iterating over it, which can cause many issues.

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What Does the Python "List index out of range" Error Mean?

An index error stands between you and a fully functional program... what will you do?

So you were working with a list or array in Python and probably tried to slice it. But instead of the expected result, you get an error that says, "list index out of range." No worries, it can happen to anyone.

Let's explore what this error means, its cause, and how to remove it without any further ado.

What Does the "list index out of range" Error Mean in Python?

When Python throws a "list index out of range" error, it means you tried to slice the list beyond its last index.

Python identifies each item in a list by its index. And the index of a list starts from zero. For instance, when you have a list with five items, its first item is on index zero, while the last is on the fourth index.

For example, in a list of five programming languages:

The indexing for the above list is between zero and four. So trying to slice it to print the fifth item as demonstrated below gives an error:

In the above example, Python tries to look for the fifth index in the list, and when it can't find it, it throws the list index error. That's because the first element (Python) is on index zero, while the last (Perl) is on index four.

That's the basis of the "list index out of range" error. As said, Python throws it whenever you try to slice a list beyond its last index.

How to Remove the "list index out of range" Error in Python

So how can you remove this error? It's easy.

Further to the previous section above, you can print the indexes using a for loop in a list comprehension :

The index of a list is the basis of slicing in programming. So since you know the highest index of the list for the output above (4), you can decipher the slice limit.

Hence, to slice the list and get the last item:

It now outputs the correct result.

What if You Want to Loop Through the List Using Its Index?

Besides the regular Python for loop , you can also use the index concept to iterate through a list. While this method may look arduous, sometimes it's unavoidable. For instance, it comes in handy if you want to sort a list in reverse order.

This method works by setting an initial index and incrementing or decrementing it by one until the last available index.

To print the items with an increasing index number (the first to the last item), for example:

But what happens if you set the initial index to one instead of zero? Have a look:

In the above example, the indexing starts from the second item (index one, Go ). So while incrementing, the loop doesn't stop until it completes the count for the five items. This forces the index to increase by one until the last item.

Hence, the slice hits a fifth index which isn't available. So it throws an index error. It means the index increases in the following pattern for each item:

Instead of the correct pattern, which is:

As you can see, the highest value of the above index is four, which is correct since the loop starts to increment the indexing from zero.

Therefore, setting the initial index to zero as you did in the first example in this section removes the "list index out of range" error:

To apply this concept for outputting the items in reverse order, you'll need to subtract one from the array's length. So this forces the index to start from four and count down to the first index, zero.

This is helpful if you're not sure about the length value of the list coming from a source, say, a database.

Here's an example:

But failing to subtract one from the length of the list throws the "list out of range index" error:

The above code throws an index error because the length of the list is five, and it tries to start indexing down from five to zero, whereas the highest index is four. So it means the list doesn't have a fifth index (sixth item).

Get Creative Handling Lists in Python

Python's errors are human-friendly and typically readable. Invariably, this makes them traceable to a reasonable extent.

As you've learned, removing the list index out of range error is pretty easy. If you face this error in your future programs, regardless of how complex the list is, you can apply the concepts explained in this post to solve the problem.

Feel free to get creative with complex lists. You might also want to learn how to sort lists in Python in your free time to get a better hang of it all.

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