Python String replace() Method

The string replace() method returns a copy of the string where occurrences of a substring are replaced with another substring.

Example:

string = "Hello World"
new_string = string.replace("Hello", "Good Bye")

print(new_string)

Good Bye World

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:

string = "Replace"
new_string = string.replace("Replace", "Replaced")

print(new_string)

Replaced

More Examples of String replace() Method 

In this section, we will see different examples of Python string replacement.

Example:

string = "Good Morning"
new_string = string.replace("Good", "Great")

print(new_string)

Great Morning

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:

string = "grrks FOR grrks"

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

print(string)
print(new_string)

grrks 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:

string = "geeks for geeks \ngeeks for geeks"

print(string)

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

geeks 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.

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))

gaaks 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.

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)

geexs for geexs 

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:

• Replace all occurrences of a substring in a string
• Replace substring in list of strings
• Replace multiple characters at once
•  Case insensitive string replacement

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