Python throws the IndexError: They’re raised when you try to access an index value inside a Python list that does not exist. For example, if you try to access the list element with index 100 but your lists consist only of three elements, Python will throw an IndexError telling you that the list index is out of range.

For the following circumstances, you could get the IndexError: list index out of range error:

  • Attempting to obtain an index from a list that doesn’t exist.
  • Using invalid indexes in your loops.
  • Utilizing the range() function with a range that is larger than the indexes in a list.

How Does Indexing Work in Python Lists?

Consider the list below:

languages = ['Python', 'JavaScript', 'Java']

print(languages[1])
# JavaScript

In the aforementioned example, there is a list of named languages. There are three entries on the list: “Python,” “JavaScript,” and “Java.” We utilized the second item’s index, languages[1], to get to it. Some newcomers could misunderstand this. They could believe that since the index is 1, the first item should be it. This is a breakdown of the list’s elements by their indexes to help you comprehend it better:

Python (item 1) => Index 0
JavaScript (item 2) => Index 1
Java (item 3) => Index 2

The first item, as you can see above, has an index of 0. You utilize an item’s index to get access to it in a list.

What Would Happen If You Attempt to Employ an Out-of-Range Index in a Python List?

An Error will appear if you try to access a list item using an index that is out of range. Here’s an illustration:

languages = ['Python', 'JavaScript', 'Java']

print(languages[3])
# IndexError: list index out of range

We attempted to access a fourth item in the aforementioned example using its index: languages[3]. The list only has three items, hence we get the IndexError: list index out of range error. The simple solution is to always try to access items in a list using an index that is already present in the list.

How to Fix the IndexError: list index out of range Error in Python Loops

In the example that follows, we’ll use a while loop to attempt to display every object in a list.

languages = ['Python', 'JavaScript', 'Java']

i = 0

while i <= len(languages):
    print(languages[i])
    i += 1

# IndexError: list index out of range

The code above returns the IndexError: list index out of range error. Let’s dissect the code to determine what transpired.

A variable named I was initially created with the value 0: i = 0.
The mistake is caused by the subsequent condition we provided for a while loop: while i <= len(languages).
We can infer from the condition that “this loop should continue to execute so long as i is less than or equal to the length of the language array.” The len() function returns the size of the list. In this case, 3 will be returned. So the condition will be this: while i <= 3. The loop will stop when i is equal to 3. Let’s pretend to be the Python compiler. Here’s what happens as the loop runs. Here’s the list: languages = [‘Python’, ‘JavaScript’, ‘Java’]. It has three indexes — 0, 1, and 2.4

When i is 0 => Python

When i is 1 => JavaScript

When i is 2 => Java

When i is 3 => Index not found in the list. IndexError: list index out of range error thrown.

So the error is thrown when i is equal to 3 because there is no item with an index of 3 in the list. We can modify the condition of the loop by removing the equal to sign, to fix this problem. When the cycle reaches the last number, this will cause it to end.

Here’s how:

languages = ['Python', 'JavaScript', 'Java']

i = 0

while i < len(languages):
    print(languages[i])
    i += 1
    
    # Python
    # JavaScript
    # Java

Now, the condition is represented as while i < 3.

The condition prevents the loop from equating to the number given by the len() method, so it will end at 2 instead.

How to Fix the IndexError: list index out of range Error in When Using the range() Function in Python

The range() function by default gives a “range” of defined integers beginning with zero. Here is an illustration of how to use the range() function:

for num in range(5):
  print(num)
    # 0
    # 1
    # 2
    # 3
    # 4

The sample above shows that range(5) gives 0, 1, 2, 3, and 4.
To print the elements in a list, combine a loop and the range() method. The first example will show a code block that throws the IndexError: list index out of range error. We’ll identify the cause of the mistake and then rectify it.

languages = ['Python', 'JavaScript', 'Java']


for language in range(4):
  print(languages[language])
    # Python
    # JavaScript
    # Java
    # Traceback (most recent call last):
    #   File "<string>", line 5, in <module>
    # IndexError: list index out of range

The aforementioned example displays the IndexError: list index out of range error along with each object in the list. Because range(4) gives 0, 1, 2, or 3, we encountered a mistake. There is no number on our roster with the value of 3. You can correct this by changing the range() function’s argument. Using the list’s length as the range() function’s argument is a preferable option.

Which is:

languages = ['Python', 'JavaScript', 'Java']


for language in range(len(languages)):
  print(languages[language])
    # Python
    # JavaScript
    # Java

Because the len() method gives 3, the aforementioned code executes without any issues. Using that with range(3) returns 0, 1, 2 which matches the number of items in a list.

Summary

Make sure you are not attempting to reach a nonexistent object in a list to resolve the “IndexError: list index out of range” error.

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