Python : How to replace single or multiple characters in a string ?

In this article we will discuss how to replace single or multiple characters in a string in Python.

Python provides a str.replace() function i.e.

str.replace(old, new , count)

It returns a new string object that is a copy of existing string with replaced content. Also,

• If count is not provides then it will return a string with all the occurrences of ‘old’, replaced with ‘new’ string.
• If count parameter is passed then it will return a string with first ‘count’ occurrences of ‘old’ string replaced with ‘new’ string.

Let’s understand by examples,

Replace all occurrences of given character / string in a string

Suppose we have a string i.e.

mainStr = "Hello, This is a sample string"

Now, lets replace all the occurrences of ‘s’ with ‘X’ i.e.

'''
Replace all occurrences of given character or string in main string
'''
otherStr = mainStr.replace('s' , 'X') 

Contents of otherStr is as follows,

Hello, ThiX iX a Xample Xtring

As strings are immutable in Python, so we can not change its content. Therefore member functions like replace() returns a new string.
As we have not provided the count parameter in replace() function. So, it will replace all the occurrences of ‘s’ with ‘X’. But what if we want to replace only first few occurrences instead of all? Let’s see how to do that,

Replace first n occurrences of given character / sub string in a string

Suppose we have a string i.e.

mainStr = "Hello, This is a sample string"

Now, lets replace first 2 occurrences of ‘s’ with ‘XXXS’ i.e.

'''
Replace First 2 occurrences of given character or string in main string
'''
otherStr = mainStr.replace('s' , 'XXXS', 2) 

Contents of otherStr is as follows,

Hello, ThiXXXS iXXXS a sample string

As we have passed the count parameter as 2, so only first 2 occurrences of ‘s’ will be replaced in the returned copy.

Replace multiple characters/strings in a string

str.replace() function can replace the occurrences of one given sub string only. But what if we want to replace multiple sub strings in a given string ?

Suppose we have a string i.e.

mainStr = "Hello, This is a sample string"

Now, how to replace all the occurrences of these three characters ‘s’, ‘l’, ‘a’ with this string ‘AA’ ?
Let’s create a new function over replace() to do that i.e.

'''
Replace a set of multiple sub strings with a new string in main string.
'''
def replaceMultiple(mainString, toBeReplaces, newString):
    # Iterate over the strings to be replaced
    for elem in toBeReplaces :
        # Check if string is in the main string
        if elem in mainString :
            # Replace the string
            mainString = mainString.replace(elem, newString)
    
    return  mainString

It will replace all the occurrences of strings in List toBeReplaces with newString in the main given list mainString.
Let’s see how to replace the occurrences of [‘s’, ‘l’, ‘a’] with “AA” i.e.

'''
Replace multiple characters / strings from a string
'''
# Replace all the occurrences of string in list by AA in the main list 
otherStr = replaceMultiple(mainStr, ['s', 'l', 'a'] , "AA")

Contents of otherStr is as follows,

HeAAAAo, ThiAA iAA AA AAAAmpAAe AAtring

Complete example is as follows,

'''
Replace a set of multiple sub strings with a new string in main string.
'''
def replaceMultiple(mainString, toBeReplaces, newString):
    # Iterate over the strings to be replaced
    for elem in toBeReplaces :
        # Check if string is in the main string
        if elem in mainString :
            # Replace the string
            mainString = mainString.replace(elem, newString)
    
    return  mainString     

def main():
    
    mainStr = "Hello, This is a sample string"

    '''
    Replace all occurrences of given character or string in main string
    '''
    otherStr = mainStr.replace('s' , 'X') 
     
    print("String with replaced Content : " , otherStr) 
    
    '''
    Replace First 2 occurrences of given character or string in main string
    '''
    otherStr = mainStr.replace('s' , 'XXXS', 2) 
     
    print(otherStr) 
    
    
    '''
    Replace multiple characters / strings from a string
    '''
    # Replace all the occurrences of string in list by AA in the main list 
    otherStr = replaceMultiple(mainStr, ['s', 'l', 'a'] , "AA")
    
    print(otherStr)
           
if __name__ == '__main__':
    main()

Output:

String with replaced Content :  Hello, ThiX iX a Xample Xtring
Hello, ThiXXXS iXXXS a sample string
HeAAAAo, ThiAA iAA AA AAAAmpAAe AAtring