Python String replace() Method
Last Updated :
05 Jul, 2024
The string replace() method returns a copy of the string where occurrences of a substring are replaced with another substring.
Example:
Python
string = "Hello World"
new_string = string.replace("Hello", "Good Bye")
print(new_string)
What is String replace() Method?
String replace() is a built-in function in Python and it is used to replace a substring with another string. It will replace every occurrence of that substring, so it should be used with caution.
It does not change the original string but returns a new one. It is mostly used in string substitution.
String replace() Method 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.
How to Use String replace() Function
You can easily use the replace() function, you just need to call the function with a string object and pass the strings as a parameter. The first parameter is the substring you want to replace, and the second parameter is the string you want to replace with.
Let’s understand it better how to replace a string in Python with a simple example:
Python
string = "Replace"
new_string = string.replace("Replace", "Replaced")
print(new_string)
More Examples of String replace() Method
In this section, we will see different examples of Python string replacement.
Example:
Python
string = "Good Morning"
new_string = string.replace("Good", "Great")
print(new_string)
1. Replace all Instances of a Single Character in a String
In this example, we are only replacing a single character from a given string. The Python string replacement approach using the replace() method is case-sensitive, and therefore it performs a case-sensitive substring substitution, i.e. R in FOR is unchanged.
Example:
Python
string = "grrks FOR grrks"
# replace all instances of 'r' (old) with 'e' (new)
new_string = string.replace("r", "e" )
print(string)
print(new_string)
Outputgrrks FOR grrks
geeks FOR geeks
Time Complexity: O(n)
Space Complexity: O(n)
2. Replace all Instances of a String in a String
Here, we will use the Python string replacement approach using replace() to replace all the geeks with GeeksforGeeks using the replace() function.
Example:
Python
string = "geeks for geeks \ngeeks for geeks"
print(string)
# Prints the string by replacing only
# 3 occurrence of Geeks
print(string.replace("geeks", "GeeksforGeeks"))
Outputgeeks for geeks
geeks for geeks
GeeksforGeeks for GeeksforGeeks
GeeksforGeeks for GeeksforGeeks
Time Complexity: O(m*n)
Space Complexity: O(n)
3. Replace only a Certain Number of Instances in a String
In this example, we will use the Python string replacement approach using replace() replacing certain numbers of words. i.e. “ek” with “a” with count=3 .
Python
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))
Outputgaaks for gaaks gaaks gaaks gaaks
geas for geas geas geeks geeks
Time Complexity: O(n)
Space Complexity: O(n)
4. Replace String using a List Comprehension and join() Method
Here, we will do string replacement without using replace(). First, we will split the original string into a list of substrings using the split() method . Then 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.
Python
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)
Time Complexity: O(n)
Space Complexity: O(n)
We have covered the definition, syntax, and examples of the string replace() method in Python. We also saw a technique to replace string without using the replace() function.
String replacement is a very important operation on strings. It is very easy and simple to use.
Read Other String Methods
Similar Reads:
Python String replace() Method – FAQs
What is replace() in Python?
replace() is a built-in string method in Python used to create a new string by replacing occurrences of a substring with another substring.
How to replace a string expression in Python?
You can use the replace() method to replace a substring with another substring in a string.
original_string = "Hello, world!"
new_string = original_string.replace("world", "Python")
print(new_string) # Output: Hello, Python!
How to change a string in Python?
In Python, strings are immutable , meaning you cannot change them in place. Instead, you create a new string with the desired changes using methods like replace().
original_string = "Hello, world!"
new_string = original_string.replace("world", "Python")
print(new_string) # Output: Hello, Python!
Can strings in Python be replaced?
Yes, strings in Python can be replaced using methods like replace() to create new strings with desired modifications.
How to replace characters in a string?
To replace characters in a string, use the replace() method with the characters you want to replace and their replacements.
original_string = "apple"
new_string = original_string.replace("a", "b")
print(new_string) # Output: bpple
