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:
Python3
string = "Hello World"
new_string = string.replace( "Hello" , "Good Bye" )
print (new_string)
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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:
Python3
string = "Replace"
new_string = string.replace( "Replace" , "Replaced" )
print (new_string)
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More Examples of String replace() Method
In this section, we will see different examples of Python string replacement.
Example:
Python3
string = "Good Morning"
new_string = string.replace( "Good" , "Great" )
print (new_string)
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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:
Python3
string = "grrks FOR grrks"
new_string = string.replace( "r" , "e" )
print (string)
print (new_string)
|
Output
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:
Python3
string = "geeks for geeks \ngeeks for geeks"
print (string)
print (string.replace( "geeks" , "GeeksforGeeks" ))
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Output
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.
Python3
string = "geeks for geeks geeks geeks geeks"
print (string.replace( "e" , "a" ))
print (string.replace( "ek" , "a" , 3 ))
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Output
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.
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)
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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
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Last Updated :
20 Dec, 2023
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