How to Replace an Element in Python List

1. Find and Replace the Python List Elements With the List Indexing Method
2. Find and Replace the Python List Elements With the for Loop Method
3. Find and Replace the Python List Elements With the List Comprehension Method
4. Find and Replace the Python List Elements With the map Method
5. Remarks

We could replace elements in a Python list in several ways. We can use Python list elements indexing, for loop, map function, and list comprehension methods.

This article will discuss the above methods to find and replace the Python list elements.

Find and Replace the Python List Elements With the List Indexing Method

Let’s take the below list as an example.

my_list = [5, 10, 7, 5, 6, 8, 5, 15]

We will change the element at the index 0 from 5 to 20.

The example code is as follows.

my_list = [5, 10, 7, 5, 6, 8, 5, 15]
my_list[0] = 20

print(my_list)

Output:

[20, 10, 7, 5, 6, 8, 5, 15]

Find and Replace the Python List Elements With the for Loop Method

We use the enumerate() function in this method. It returns a enumerate object that also contains the counter together with the elements. When we combine the enumerate() function with the for loop, it iterates the enumerate object and gets the index and element together.

The code is:

my_list = [5, 10, 7, 5, 6, 8, 5, 15]
for index, value in enumerate(my_list):
    if value == 5:
        my_list[index] = 9

print(my_list)

Output:

[9, 10, 7, 9, 6, 8, 9, 15]

Find and Replace the Python List Elements With the List Comprehension Method

In this method, we can generate a new list by applying pre-defined conditions on the old list.

The Syntax is:

my_list = [5, 10, 7, 5, 6, 8, 5, 15]

[9 if value == 5 else value for value in my_list]

print(my_list)

Output:

[9, 10, 7, 9, 6, 8, 9, 15]

Find and Replace the Python List Elements With the map Method

This method changes the entries of the second list with the index of the first list items.

The code is:

list_1 = [5, 10, 7]
list_2 = [7, 10, 7, 5, 7, 5, 10]

ent = {k: i for i, k in enumerate(list_1)}
result = list(map(ent.get, list_2))

print("list2 after replacement is:", result)

Output:

list2 after replacement is: [2, 1, 2, 0, 2, 0, 1]

Remarks

1. List indexing method is good when we replace one element in a list.
2. List comprehension method is the right choice when we replace multiple elements in a list based on selective criteria.
3. Loop methods are discouraged, as it takes more execution time and memory.