Fundamentals of Python Programming

Everything you need to know about Strings in Python

Board Infinity
Board Infinity
Everything you need to know about Strings in Python

    A-Z about Python Variables

    Python data Types

    String Concatenation in Python

    String formatting in Python

    Python print() Function

    Everything you need to know about Strings in Python

    Not Equal Operator in Python

    How to sort string in Python?

    Python For Loop

    Python While Loop

    Everything You Need to Know About Tuples in Python | Data Science

    Learn Different Methods to convert a List into a Tuple in Python

    List Slicing in Python

    Converting String to Float in Python

    List Index Out of Range Error in Python

    Python Sort() Function

    Python 2D Array

    How to Remove Key from Python Dictionary?

    Python dictionary values()

    Converting String to Dictionary in Python

    Bytes to String in Python

    Python reduce() function

    What are defaultdict in Python?

    Generators in Python

    Learn about range() in Python

    Python numpy.linspace()

    Exit Command in Python

    Python Virtual Environment

Introduction

A Python string is one of the standard datatypes of Python. First, let us understand what a “string” means.

We define a string as a sequence of characters. By characters, we mean alphabets, digits, symbols, and special characters. A typical Python string is enclosed within single quotes or double quotes or even triple quotes. Strings can also span over multiple lines as depicted below

The utmost important characteristic is that it is an “immutable datatype”. An immutable datatype is a datatype whose value cannot be changed after the assignment of it

Let us understand how to initialize a string through an example :

Example

str = "Board Infinity"

str1 = 'Board Infinity'

str2 = '''Board

Infinity'''

print(str)

print(str1)

print(str2)

write your code here: Coding Playground

Output

The further section dwells on the various operations that can be performed on it

Accessing The Elements of a String

The individual characters of a string are indexed or in layman’s terms numbered starting from 0 to the length of the string - 1. With the help of this unique number, we have access to all characters of a string.

For example, the number 0 corresponds to the first character, 1 to the second character, and so on. Another feature supported by Python is negative indexing, which means the individual characters are indexed by negative numbers such as -1 corresponding to the last character, -2 to the second last character, and so on.

The diagram illustrates the indexing of a string indicating both positive as well as negative indexing

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

B

O

A

R

D

I

N

F

I

N

I

T

Y

0

1

2

3

4

5

6

7

8

9

10

11

12

Traversing Through a String

Traversal through a string refers to iterating through a string - one character at a time

Let us consider the following code snippet in which we print the string character by character

Example

str = "Board Infinity"

for i in range(len(str)):

print(str[i],end = " ")

Output

Quick Activity: Try printing the characters of a string in the reverse order using negative indexing

str = "Board Infinity"

for i in range(len(str)-1,-1,-1):

print(str[i],end = " ")

Output

String Slicing

Sometimes, we may need to access a specific sequence of characters as opposed to a single character by indexing, this is where string slicing comes into play. The range of characters is specified within square brackets of the form [m:n]. The characters starting from the mth index to (n-1)th index will be selected.

If the value of m is not specified, 0 indexes are taken by default and on the other hand, if the value of n is not specified the (length -1) value will be taken by default

Let us understand this through an example:

str = "Board Infinity"

print(str[2:5]) # Printing 3rd to 4th Character

print(str[:6])  # Printing from start to 5th Character

print(str[7:])  # Printing from 7th Character to the end

Output

Formatting of Strings

Python allows you to format your strings using the built-in format method. The format method contains curly braces which correspond to a specific keyword pair or a position or to the word itself. This is illustrated by the following code snippet

# (Corresponds to the word itself)

str1 = "{} {} ".format('Board', 'Infinity')

print(str1)

# By Position (Corresponds to the position)

str1 = "{1} {0} ".format('Board', 'Infinity')

print(str1)

# By Keyword Pair (Corresponds to the keyword pair)

str1 = "{b} {i}".format(b='Board', i='Infinity')

print(str1)

write your code here: Coding Playground

Output

Updating/Deleting a Python String

Strings in Python are immutable, that is we cannot change the value of the individual character in place. So how do we modify strings?

This can be achieved through string slicing and concatenation as discussed previously. Concatenation if you don’t know refers to the act of joining two strings together

Example: “Board” + “Infinity” = “BoardInfinity”

Example: Consider the string “BoardqInfinity”, we would like to remove the character q from the string which can be done by the code snippet below:

str = "BoardqInfinity"

str = str[:5] + str[6:]

print(str)

Output

Similarly, if we would like to add a space between the words it can be done in a similar manner as well

str = "BoardInfinity"

str = str[:5] + " " + str[5:]

print(str)

Output

Moreover, the entire string itself can be changed but not a single character directly. The following code demonstrates this:

str = "BoardInfinity"

print("Before = ",str)

str = "InfinityBoard"

print("After = ",str)

Output

In addition, the entire string can be deleted with the help of the del keyword. However, once deleted it is not possible to print it as it no longer exists.

str = "BoardInfinity"

del str

String Methods in Python

Python provides an inbuilt method for the manipulation as well as performing various operations on the string. Some of them are listed below for your reference:

Function

Syntax

Functionality

lower()

string.lower()

Converts all characters to lower case

upper()

string.upper()

Converts all characters to upper case

title()

string.title()

Converts all characters to title case

isdigit()

string.isdigit()

Returns True if all characters of the string are digits

isalpha()

string.isalpha()

Returns True if all characters of the string are alphabets

isspace()

string.isspace()

Returns true if the string is an empty space 

captialize()

string.capitalize()

Converts the first character of the string to an uppercase

strip()

string.strip([chars])

Returns the string after converting the first character of the string to uppercase

Thus, by the end of this tutorial, you would have developed a good understanding of strings in Python regarding how to access them, format them as well as manipulate them.