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:

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:

Replaced

More Examples of String replace() Method 

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

Example:

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:

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:

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.

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.

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