How to Replace Values in a List in Python? - GeeksforGeeks

22 Nov, 2021
In this article, we are going to see how to replace the value in a List using Python. We can replace values in the list in serval ways. Below are the methods to replace values in the list.
Using list indexing
Using for loop
Using while loop
Using lambda function
Using list slicing
We can access items of the list using indexing. This is the simplest and easiest method to replace values in a list in python. If we want to replace the first item of the list we can di using index 0. Here below, the index is an index of the item that we want to replace and the new_value is a value that should replace the old value in the list.
Syntax:  l[index]=new_value
Code:
Python3
# Replace Values in a List using indexing  # define listl = [ 'Hardik','Rohit', 'Rahul', 'Virat', 'Pant']  # replace first valuel[0] = 'Shardul'  # print listprint(l)
Output:
['Shardul', 'Rohit', 'Rahul', 'Virat', 'Pant']
We can use for loop to iterate over the list and replace values in the list. Suppose we want to replace ‘Hardik’ and ‘Pant’ from the list with ‘Shardul’ and ‘Ishan’. We first find values in the list using for loop and if condition and then replace it with the new value. 
Python3
# Replace Values in a List using For Loop  # define listl = ['Hardik', 'Rohit', 'Rahul', 'Virat', 'Pant']  for i in range(len(l)):      # replace hardik with shardul    if l[i] == 'Hardik':        l[i] = 'Shardul'      # replace pant with ishan    if l[i] == 'Pant':        l[i] = 'Ishan'  # print listprint(l)
Output:
['Shardul', 'Rohit', 'Rahul', 'Virat', 'Ishan']
We can also use a while loop to replace values in the list. While loop does the same work as for loop. In the while loop first, we define a variable with value 0 and iterate over the list. If value matches to value that we want to replace then we replace it with the new value.
Python3
# Replace Values in a List using While Loop  # define listl = ['Hardik', 'Rohit', 'Rahul', 'Virat', 'Pant']  i = 0while i < len(l):      # replace hardik with shardul    if l[i] == 'Hardik':        l[i] = 'Shardul'      # replace pant with ishan    if l[i] == 'Pant':        l[i] = 'Ishan'      i += 1  # print listprint(l)
Output:
['Shardul', 'Rohit', 'Rahul', 'Virat', 'Ishan']
In this method, we use lambda and map function to replace the value in the list. map() is a built-in function in python to iterate over a list without using any loop statement. A lambda is an anonymous function in python that contains a single line expression. Here we gave one expression as a condition to replace value. Here we replace ‘Pant’ with ‘Ishan’ in the lambda function. Then using the list() function we convert the map object into the list.
Syntax: l=list(map(lambda x: x.replace(‘old_value’,’new_value’),l))
Python3
# Replace Values in a List using Lambda Function  # define listl = ['Hardik', 'Rohit', 'Rahul', 'Virat', 'Pant']  # replace Pant with Ishanl = list(map(lambda x: x.replace('Pant', 'Ishan'), l))  # print listprint(l)
Output:
['Hardik', 'Rohit', 'Rahul', 'Virat', 'Ishan']
Python allows us to do slicing inside a list. Slicing enables us to access some parts of the list. We can replace values inside the list using slicing. First, we find the index of variable that we want to replace and store it in variable ‘i’. Then, we replace that item with a new value using list slicing. Suppose we want to replace ‘Rahul’ with ‘Shikhar’ than we first find the index of ‘Rahul’ and then do list slicing and remove ‘Rahul’ and add ‘Shikhar’ in that place.
Syntax: l=l[:index]+[‘new_value’]+l[index+1:]
Python3
# Replace Values in a List using Slicing  # define listl = ['Hardik', 'Rohit', 'Rahul', 'Virat', 'Pant']  # find the index of Rahuli = l.index('Rahul')  # replace Rahul with Shikharl = l[:i]+['Shikhar']+l[i+1:]  # print listprint(l)
Output:
['Hardik', 'Rohit', 'Shikhar', 'Virat', 'Pant']
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