Python String replace() Method

String replace() in Python returns a copy of the string where occurrences of a substring are replaced with another substring. 

Syntax of String replace() method

The replace() method in Python strings has the following syntax:

Syntax: string.replace(old, new, count)

Parameters: 

• old – old substring you want to replace.
• new – new substring which would replace the old substring.
• count – (Optional ) the number of times you want to replace the old substring with the new substring. 

Return Value : It returns a copy of the string where all occurrences of a substring are replaced with another substring. 

Examples of Python replace() Methods

Replace all Instances of a single character using replace() in Python

In this example, we are only replacing a single character from a given string. The Python replace() method is case-sensitive, and therefore it performs a case-sensitive substring substitution, i.e. R in FOR is unchanged.

Python3

string = "grrks FOR grrks"

# replace all instances of 'r' (old) with 'e' (new)
new_string = string.replace("r", "e" )

print(string)
print(new_string)

Output :

grrks FOR grrks
geeks FOR geeks

Replace all Instances of a String using replace() in Python

Here, we will replace all the geeks with GeeksforGeeks using replace() function.

Python3

string = "geeks for geeks \ngeeks for geeks"

print(string)

# Prints the string by replacing only
# 3 occurrence of Geeks
print(string.replace("geeks", "GeeksforGeeks"))

Output :

geeks for geeks 
geeks for geeks
GeeksforGeeks for GeeksforGeeks 
GeeksforGeeks for GeeksforGeeks

Replace only a certain number of Instances using replace() in Python

In this example, we are replacing certain numbers of words. i.e. “ek” with “a” with count=3.

Python3

string = "geeks for geeks geeks geeks geeks"

# Prints the string by replacing
# e by a
print(string.replace("e", "a"))

# Prints the string by replacing only
# 3 occurrence of ek by a
print(string.replace("ek", "a", 3))

Output:

gaaks for gaaks gaaks gaaks gaaks
geas for geas geas geeks geeks

Using a list comprehension and the join() method:

Approach:

Split the original string into a list of substrings using the split() method.
Use a list comprehension to replace each occurrence of old_substring with new_substring.
Join the list of substrings back into a string using the join() method.

Python3

my_string = "geeks for geeks "
old_substring = "k"
new_substring = "x"

split_list = my_string.split(old_substring)
new_list = [new_substring if i < len(split_list)-1 else '' for i in range(len(split_list)-1)]
new_string = ''.join([split_list[i] + new_list[i] for i in range(len(split_list)-1)] + [split_list[-1]])

print(new_string)

Output

geexs for geexs 

Time Complexity: O(n)
Space Complexity: O(n)