We are given a list of strings, and our task is to replace a specific substring within each string with a new substring. This is useful when modifying text data in bulk. For example, given a = ["hello world", "world of code", "worldwide"], replacing "world" with "universe" should result in ["hello universe", "universe of code", "universewide"]. Let's discuss different methods to do this in Python.

Using List Comprehension with replace()

replace() method replaces occurrences of a substring in a string. Using list comprehension, we can apply it to every string in the list efficiently.

a = ["hello world", "world of code", "worldwide"]  
old_substring = "world"  
new_substring = "universe"  

res = [s.replace(old_substring, new_substring) for s in a]  
print(res) 

['hello universe', 'universe of code', 'universewide']

Explanation:

• The replace() function replaces all occurrences of "world" with "universe" in each string.
• List comprehension iterates through the list and applies replace() to every string.

Using map()

map() function applies replace() to each string in the list without using explicit loops.

a = ["hello world", "world of code", "worldwide"]  
s1 = "world"  
s2 = "universe"  

res = list(map(lambda s: s.replace(s1, s2), a))  
print(res)

['hello universe', 'universe of code', 'universewide']

Explanation:

• map() applies the replace() function to each string in a.
• The lambda function takes each string and replaces "world" with "universe".
• list(map(...)) ensures that the result is stored as a list.

Using for Loop and replace()

A for loop allows modifying the list step by step, storing results in a new list.

a = ["hello world", "world of code", "worldwide"]  
s1 = "world"  
s2 = "universe"  

res = []  
for s in a:  
    s3 = s.replace(s1, s2) 
    res.append(s3)  

print(res)

['hello universe', 'universe of code', 'universewide']

Explanation:

• The for loop iterates over each string in a.
• s.replace(s1, s2) replaces "world" with "universe" in each string.
• The modified string is stored in result using append().

Using re.sub() for Pattern-Based Replacement

re.sub() function allows replacing substrings based on patterns.

import re  

a = ["hello world", "world of code", "worldwide"]  
s1 = "world"  
s2 = "universe"  

res = [re.sub(s1, s2, s) for s in a]  
print(res)  

['hello universe', 'universe of code', 'universewide']

Explanation:

• re.sub(pattern, replacement, string) replaces "world" with "universe" in each string.
• This method is useful when replacing text based on complex patterns rather than exact substrings.

Using str.translate()

If replacing single characters instead of substrings, str.translate() is a faster alternative.

a = ["hello world", "world of code", "worldwide"]  

trans_table = str.maketrans("o", "0")  

res = [s.translate(trans_table) for s in a]  
print(res) 

['hell0 w0rld', 'w0rld 0f c0de', 'w0rldwide']

Explanation:

• str.maketrans("o", "0") creates a mapping to replace "o" with "0".
• s.translate(trans_table) applies this mapping to each string in a.
• This method is limited to character replacements rather than full substrings.

Related Articles:

• Python Lists
• Python String
• List Comprehension in Python
• Python String replace() Method
• Python map() function
• Python For Loops
• re.sub() - Python RegEx
• Python String translate() Method