How to Fix Python IndexError: list assignment index out of range

1. Python IndexError: list assignment index out of range
2. Fix the IndexError: list assignment index out of range in Python
3. Fix IndexError: list assignment index out of range Using append() Function
4. Fix IndexError: list assignment index out of range Using insert() Function
5. Conclusion

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.

Python IndexError: list assignment index out of range

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

Code Example:

# error program --> IndexError: list assignment index out of range
i = [7, 9, 8, 3, 7, 0]  # index range (0-5)
j = [1, 2, 3]  # index range (0-3)

print(i, "\n", j)
print(f"\nLength of i = {len(i)}\nLength of j = {len(j)}")

print(f"\nValue at index {1} of list i and j are {i[1]} and {j[1]}")
print(
    f"\nValue at index {3} of list i and j are {i[3]} and {j[3]}"
)  # error because index 3 isn't available in list j

Output:

[7, 9, 8, 3, 7, 0]
[1, 2, 3]

Length of i = 6
Length of j = 3

Value at index 1 of list i and j are 9 and 2

IndexError: list assignment index out of range

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.

Fix the IndexError: list assignment index out of range in Python

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.

Code Example:

a = [1, 2, 3, 4, 5, 6]
b = []
k = 0

for l in a:
    b[k] = l  # indexError --> because the length of b is 0
    k += 1

print(f"{a}\n{a}")

Output:

IndexError: list assignment index out of range

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().

Fix IndexError: list assignment index out of range Using append() Function

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.

Code Example:

a = [1, 2, 3, 4, 5, 6]
b = []
k = 0

for l in a:
    # use append to add values at the end of the list
    j.append(l)
    k += 1

print(f"List a: {a}\nList b: {a}")

Output:

List a: [1, 2, 3, 4, 5, 6]
List b: [1, 2, 3, 4, 5, 6]

Fix IndexError: list assignment index out of range Using insert() Function

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

Code Example:

a = [1, 2, 3, 5, 8, 13]
b = []
k = 0

for l in a:
    # use insert to replace list a into b
    j.insert(k, l)
    k += 1

print(f"List a: {a}\nList b: {a}")

Output:

List a: [1, 2, 3, 4, 5, 6]
List b: [1, 2, 3, 4, 5, 6]

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.

Code Example:

a = [1, 2, 3, 4, 5, 6]
b = [None] * len(i)

print(f"Length of a: {len(a)}")
print(f"Length of b: {len(b)}")

print(f"\n{a}\n{b}")

Output:

Length of a: 6
Length of b: 6

[1, 2, 3, 4, 5, 6]
[None, None, None, None, None, None]

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

Conclusion

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.