Python String Builder Equivalent [Complete Guide]

Immutability of String in python

In python, strings are immutable which means once the string is defined or created it cannot be modified using indexing or concatenation.

The generic way of modifying string using the indexes is invalid in python and throws a type error when we use the index for modifying characters.


Greet = "Hello Goom !"
Greet[0] = 'B'
OutputTypeError: 'str' object does not support item assignment

What is String Builder?

String builder is a dynamic string generator in python which is used to implement the functionality of the string modification and concatenation efficiently.

String builder provides the functionality of text files to the string in python i.e File opening, closing, modification.

Why use String Builder?

The traditional methods to modify and concatenate strings take a lot of memory if the strings are modified too frequently. using the string builder this problem of memory usage is reduced and the program becomes more efficient.

For example:

greet1 = "Hello"greet2 = "Goom !"print(greet1 + greet2)
Output :
Hello Goom !

In the above example using traditional concatenation makes the python interpreter create the third variable but using the string builder technique we can convert the string to a file-like object which can be modified and concatenated easily without creating the third variable.

Working of + operator in Python:

In a traditional concatenation of strings if we declare 2 strings with some string value and print the result of concatenation directly in the print statement then the python interpreter will create a third copy of the string, concatenate the 2 string in the third string then return it to the print function


greet1 = "Hello"greet2 = "User !"print(greet1 + greet2)
Output -Hello User !

Different ways to concatenate the string (StringBuilder Equivalent):

1. join method

This method is used to join the list/array of the string/ characters in python.if you have the list of strings or characters, we can easily merge the items of the string into a single string using the join method.


words = ["hello User" , " Welcome to the Goom !", "let's start our python journey together !"]
sentence = " ".join(words)


Hello User Welcome to the Goom ! Let's start our python journey together! 

2. format method

This method uses the concept of placeholders to modify and concatenate the string in different ways.

We define the variables as placeholders In curly brackets {} inside the final string. While printing these strings the python interpreter will swap these variables inside the curly brackets with their values.


user1 = "Jack"
user2 = "Mark"
welcome_greet = "hello {} ! Meet your colleague {}".format(user1 , user2)

Hello Jack ! Meet your colleague Mark.

3. f-strings method

The f-string methods are very similar to format methods as they both use the concept of placeholders .fstring is the updated version of the format method to concatenate and modify string dynamically.


user1 = "Jack"
user2 = "Mark"
welcome_greet = f"Hello {user1} ! Meet your colleague {user2}"

Hello Jack ! Meet your colleague Mark

StringBuilder Method io and cStringIO

The io and cStringIO module in python is used to provide the functionality to string to work like a word file.

This is very useful when a developer is working with a large-size string that takes a decent amount of memory and time to copy and append to another string.

Difference between IO and cStringIO

The main difference between IO and cstringIO is their implementation:

  • The io module is implemented using the basic blocks of python while The cStringIO module is implemented using the components of C programming languages.
  • Both modules provide the same functionality for working with in-memory strings and contain write and get values. However, the string module is faster due to its C-based implementation.

#cStringIO is only available in python 2. x it Is removed from python 3. x

Implementation of IO module:

import io

build_obj = io.StringIO()
build_obj.write("Hello User !")
build_obj.write("Welcome to Goom !")
build_obj.write("We hope you are enjoying here")

introduction = build_obj.getvalue()

Hello User !Welcome to Goom ! We hope you are enjoying here

Python StringBuilder Equivalent Use Cases:

1. Maintain logging of users

This is useful for various websites which store the information of every user that visits there. Using the string builder we can store the names of all the users who visited the website inside a single string.


import io

builder = io.StringIO()

def add_name(name):
   builder.write(name +"")

log_entry = builder.getvalue()

print("Total User Logged In :")
Output -Total User Logged In :MarkDaisyKyle

2. Dynamic HTML generation:

When creating the dynamic websites developer needs to update the content of the website depending on the user input. Dynamic content creation can be achieved simply using the string builder method.

For example:

import io

topics =["Python String","Python List", "Python Dictionary","Python Set","Python File"]

def add_topic(topic):

def convert():
    build_obj = io.StringIO()
    for topic in topics:
    html = build_obj.getvalue()
return htmladd_topic("Errors")

html = convert()
print("Dynamically Generated Table in HTML :")
print (html)
Dynamically Generated Table in HTML :
<tr><td>Python String</td></tr>
<tr><td>Python List</td></tr>
<tr><td>Python Dictionary</td></tr>
<tr><td>Python Set</td></tr>
<tr><td>Python File</td></tr>

Errors While working with StringBuilder in Python

1. AttributeError:

This error can occur when trying to access an attribute that’s not available in the string builder class.

For example:

import io

build_obj = io.StringIO()
length = builder.size
Output:AttributeError: '_io.StringIO' object has no attribute 'size'

To fix this error, you need to access an attribute that’s available in the string builder class.

import io

build_obj = io.StringIO()
length = builder.tell()

output :1

2. TypeError

Is raised when an operation is performed that is using an incorrect or unsupported object type. For example

import io

builder = io.StringIO()
Output:ValueError: write() argument must be str, not int

Here we are trying to concatenate string objects with integer

This can be solved using type casting.

import io

builder = io.StringIO()

3. Modifying the string using indexing

import io

builder = io.StringIO()
message = 'Hello, Goom!'

output:TypeError: 'str' object does not support item assignment

As we already know, strings in python are immutable so updating them using indexing is not possible.

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