List assignment index out of range python ошибка

In python, lists are mutable as the elements of a list can be modified. But if you try to modify a value whose index is greater than or equal to the length of the list then you will encounter an Indexerror: list assignment index out of range.  

Python Indexerror: list assignment index out of range Example

If ‘fruits’ is a list, fruits=[‘Apple’,’ Banana’,’ Guava’]and you try to modify fruits[5] then you will get an index error since the length of fruits list=3 which is less than index asked to modify for which is 5.

Output:

Traceback (most recent call last):
 File "/example.py", line 3, in <module>
   fruits[5]='Mango'
IndexError: list assignment index out of range

So, as you can see in the above example, we get an error when we try to modify an index that is not present in the list of fruits.

Python Indexerror: list assignment index out of range Solution

Method 1: Using insert() function

The insert(index, element) function takes two arguments, index and element, and adds a new element at the specified index.

Let’s see how you can add Mango to the list of fruits on index 1.

Output:

Original list: ['Apple', 'Banana', 'Guava']
Modified list: ['Apple', 'Mango', 'Banana', 'Guava']

It is necessary to specify the index in the insert(index, element) function, otherwise, you will an error that the insert(index, element) function needed two arguments.

Method 2: Using append()

The append(element) function takes one argument element and adds a new element at the end of the list.

Let’s see how you can add Mango to the end of the list using the append(element) function.

Output:

Original list: ['Apple', 'Banana', 'Guava']
Modified list: ['Apple', 'Banana', 'Guava', 'Mango']

Python IndexError FAQ

Q: What is an IndexError in Python?

A: An IndexError is a common error that occurs when you try to access an element in a list, tuple, or other sequence using an index that is out of range. It means that the index you provided is either negative or greater than or equal to the length of the sequence.

Q: How can I fix an IndexError in Python?

A: To fix an IndexError, you can take the following steps:

1. Check the index value: Make sure the index you’re using is within the valid range for the sequence. Remember that indexing starts from 0, so the first element is at index 0, the second at index 1, and so on.
2. Verify the sequence length: Ensure that the sequence you’re working with has enough elements. If the sequence is empty, trying to access any index will result in an IndexError.
3. Review loop conditions: If the IndexError occurs within a loop, check the loop conditions to ensure they are correctly set. Make sure the loop is not running more times than expected or trying to access an element beyond the sequence’s length.
4. Use try-except: Wrap the code block that might raise an IndexError within a try-except block. This allows you to catch the exception and handle it gracefully, preventing your program from crashing.

Last Updated :
30 Jun, 2023

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The reason for the error is that you’re trying, as the error message says, to access a portion of the list that is currently out of range.

For instance, assume you’re creating a list of 10 people, and you try to specify who the 11th person on that list is going to be. On your paper-pad, it might be easy to just make room for another person, but runtime objects, like the list in python, isn’t that forgiving.

Your list starts out empty because of this:

a = []

then you add 2 elements to it, with this code:

a.append(3)
a.append(7)

this makes the size of the list just big enough to hold 2 elements, the two you added, which has an index of 0 and 1 (python lists are 0-based).

In your code, further down, you then specify the contents of element j which starts at 2, and your code blows up immediately because you’re trying to say «for a list of 2 elements, please store the following value as the 3rd element».

Again, lists like the one in Python usually aren’t that forgiving.

Instead, you’re going to have to do one of two things:

1. In some cases, you want to store into an existing element, or add a new element, depending on whether the index you specify is available or not
2. In other cases, you always want to add a new element

In your case, you want to do nbr. 2, which means you want to rewrite this line of code:

a[j]=a[j-2]+(j+2)*(j+3)/2

to this:

a.append(a[j-2]+(j+2)*(j+3)/2)

This will append a new element to the end of the list, which is OK, instead of trying to assign a new value to element N+1, where N is the current length of the list, which isn’t OK.

IndexError: list assignment index out of range

List elements can be modified and assigned new value by accessing the index of that element. But if you try to assign a value to a list index that is out of the list’s range, there will be an error. You will encounter an IndexError list assignment index out of range. Suppose the list has 4 elements and you are trying to assign a value into the 6th position, this error will be raised.

Example:

list1=[]
for i in range(1,10):
    list1[i]=i
print(list1)

Output: 

IndexError: list assignment index out of range

In the above example we have initialized a “list1“ which is an empty list and we are trying to assign a value at list1[1] which is not present, this is the reason python compiler is throwing “IndexError: list assignment index out of range”.

We can solve this error by using the following methods.

Using append()

We can use append() function to assign a value to “list1“, append() will generate a new element automatically which will add at the end of the list.

Correct Code:

list1=[]
for i in range(1,10):
    list1.append(i)
print(list1)

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9]

In the above example we can see that “list1” is empty and instead of assigning a value to list, we append the list with new value using append() function.

Using insert() 

By using insert() function we can insert a new element directly at i’th position to the list.

Example:

list1=[]
for i in range(1,10):
    list1.insert(i,i)
print(list1)

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9]

In the above example we can see that “list1” is an empty list and instead of assigning a value to list, we have inserted a new value to the list using insert() function.

Example with While loop

num = []
i = 1
while(i <= 10):
num[i] = I
i=i+1
 
print(num)

Output:

IndexError: list assignment index out of range

Correct example:

num = []
i = 1
while(i <= 10):
    num.append(i)
    i=i+1
 
print(num)

Output:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Conclusion:

Always check the indices before assigning values into them. To assign values at the end of the list, use the append() method. To add an element at a specific position, use the insert() method.