Update List Elements

In Python, elements in a list can be updated or replaced by assigning a new value to an element’s index position.

In previous articles, we covered accessing list elements by index, using the list index method to find an element’s index, and appending elements to a list. This article focuses on how to update elements in a Python list.

Table of Contents

There is no specific method required to update an element in the list. We can access an element using the index position and assign a new value at that index to update (replace) the element.

Now, let’s see how we can do this in this program.

Program – Update List Elements

# update elements in list

shbytes_list = ['Python', 'AWS', 'Java', 'Azure']
print(shbytes_list)

shbytes_list[2] = 'Machine Learning'
print(shbytes_list)

In this program, we have declared and initialized a list, which is referenced by the variable name sybytes_list. Element Java is present at index position 2. We are assigning a new value Machine Learning at index 2, which will update (replace) the previous value at index 2.

Output – Example Program – Update List Elements

['Python', 'AWS', 'Java', 'Azure']
['Python', 'AWS', 'Machine Learning', 'Azure']

In this example, the original list contains Java at index 2. After assigning a new value Machine Learning to that position, the list reflects the updated element.

Program – Update List Elements in Nested List

# Update List Elements in Nested List

nested_list = ['Python', 'AWS', 'Azure', [1, 2, 3]]
print("original nested list", nested_list)

nested_list[3][2] = 4
print("updated mixed list", nested_list)

We have declared and initialized a nested list, which is referenced by the variable name nested_list. The nested element [1, 2, 3] is at index 3 of the list. We are accessing index 3, which contains the nested list [1, 2, 3]. Then, we access index 2 of that nested list and assign its value to 4.

Note: only mutable elements of nested list can be updated. We cannot update immutable elements of a nested list.

Output – Example Program – Update Elements in Nested List

original nested list ['Python', 'AWS', 'Azure', [1, 2, 3]]
updated mixed list ['Python', 'AWS', 'Azure', [1, 2, 4]]

In the output, the last element 3 is replaced with 4 in the nested list.

Summary

This article explains how to modify elements within a Python list by accessing and reassigning values at specific index positions. We explored:

Update List Elements by index
Update List Elements in Nested List

Code snippets and programs related to Modify Elements in Python List, can be accessed from GitHub Repository. This GitHub repository all contains programs related to other topics in Python tutorial.

Interview Questions & Answers

Q: How to replace multiple elements in a list?

We can replace multiple elements in a list by assigning a slice of the list to a new list.

number_list = [10, 20, 30, 40, 50]
number_list[1:4] = [200, 300, 400]
print(number_list)     # Final number_list elements: [10, 200, 300, 400, 50]

Here, the elements from index 1 to 3 (i.e., 20, 30, and 40) are replaced with 200, 300, and 400 respectively.

Q: How can we replace all occurrences of a specific element value in a list?

There are two ways, we can replace all occurrences of a specific element in a list.

use a list comprehension to create a new list with the replacements
use a loop with condition to update the element in the same list or create a new list

number_list = [10, 20, 30, 20, 40]
for index in range(len(number_list)):
    if number_list[index] == 20:
        number_list[index] = 100
print(number_list)                    # Final elements in number_list: [10, 100, 30, 100, 40]

In this program, we have replaced all occurrences of 20 with 100 in the same number_list.

Q: If a list contains mixed data types (e.g., integers, strings), how can we replace elements without causing errors?

We need to ensure that the condition checks or replacements are type-safe, meaning they account for different data types to avoid errors:

mixed_list = [10, '20', 30, 'forty']
# Replace only integers equal to 10
for index in range(len(mixed_list)):
    if isinstance(mixed_list[index], int) and mixed_list[index] == 10:
        mixed_list[index] = 100
print(mixed_list)      # Final elements in mixed_list: [100, '20', 30, 'forty']

Here, isinstance(mixed[index], int) checks if the element is an integer before attempting it to compare with an integer value and replace it with another value.

Test Your Knowledge: Practice Quiz

Quiz on Update List Elements in Python

Test Your Knowledge: How to Update List Elements in Python

1 / 4

1. What will be the output of the following code?
count_list = [1, 2, 3]
count_list[0:2] = [10]
print(count_list)

[10]

[1, 10, 3]

[10, 2, 3]

[10, 3]

2 / 4

2. Which of the following methods can be used to remove an element from a list?

Both remove(element) and pop(index)

remove(element)

pop(index)

delete(element)

3 / 4

3. What will be the result of executing the following code?
count_list = [1, 2, [3, 4]]
count_list[2][1] = 5
print(count_list)

Error

[1, 2, [3, 4]]

[1, 2, [3, 5]]

[1, 2, [5, 4]]

4 / 4

4. What will be the output of the following code?
number_list = [1, 2, 3, 4]
number_list[2] = 10
print(number_list)

Error

[1, 10, 3, 4]

[1, 2, 10, 4]

[1, 2, 3, 4]

Your score is

Update List Elements | Modify Elements in Python List