Python - Modify Strings

String modification refers to the process of changing the characters of a string. If we talk about modifying a string in Python, what we are talking about is creating a new string that is a variation of the original one.

In Python, a string (object of str class) is of immutable type. Here, immutable refers to an object that cannot be modified in place once it’s created in memory. Unlike a list, we cannot overwrite any character in the sequence, nor can we insert or append characters to it directly. If we need to modify a string, we will use certain string methods that return a new string object. However, the original string remains unchanged.

We can use any of the following tricks as a workaround to modify a string.

Converting a String to a List

Both strings and lists in Python are sequence types, they are interconvertible. Thus, we can cast a string to a list, modify the list using methods like insert(), append(), or remove() and then convert the list back to a string to obtain a modified version.

Suppose, we have a string variable s1 with WORD as its value and we are required to convert it into a list. For this operation, we can use the list() built-in function and insert a character L at index 3. Then, we can concatenate all the characters using join() method of str class.

Example

The below example practically illustrates how to convert a string into a list.

s1="WORD"
print ("original string:", s1)
l1=list(s1)

l1.insert(3,"L")

print (l1)

s1=''.join(l1)
print ("Modified string:", s1)

It will produce the following output −

original string: WORD
['W', 'O', 'R', 'L', 'D']
Modified string: WORLD

Using the Array Module

To modify a string, construct an array object using the Python standard library named array module. It will create an array of Unicode type from a string variable.

Example

In the below example, we are using array module to modify the specified string.

import array as ar

# initializing a string
s1="WORD"
print ("original string:", s1)

# converting it to an array
sar=ar.array('u', s1)

# inserting an element
sar.insert(3,"L")

# getting back the modified string
s1=sar.tounicode()
print ("Modified string:", s1)

It will produce the following output −

original string: WORD
Modified string: WORLD

Using the StringIO Class

Python’s io module defines the classes to handle streams. The StringIO class represents a text stream using an in-memory text buffer. A StringIO object obtained from a string behaves like a File object. Hence we can perform read/write operations on it. The getvalue() method of StringIO class returns a string.

Example

Let us use the above discussed principle in the following program to modify a string.

import io

s1="WORD"
print ("original string:", s1)

sio=io.StringIO(s1)
sio.seek(3)
sio.write("LD")
s1=sio.getvalue()

print ("Modified string:", s1)

It will produce the following output −

original string: WORD
Modified string: WORLD