Topic - 3

Python String

• Till now, we have discussed numbers as the standard data types in Python. In this tutorial section, we will discuss the most popular data type in Python, i.e., string.
• Python string is the collection of characters surrounded by single quotes, double quotes, or triple quotes. The computer does not understand the feelings; internally, it stores manipulated characters as a combination of the 0's and 1's.
• Each character is encoded in the ASCII or Unicode character. We can say that Python strings are also called the collection of Unicode characters.
• A string in Python is a sequence of characters. It is enclosed in single quotes (') , double quotes (") and triple quotes(''')
• Examples: 

        #Using single quotes  

str1 = 'Welcome Python'  

print(str1)  

#Using double quotes  

str2 = "Welcome Python"  

print(str2)  

#Using triple quotes  

str3 = '''''Triple quotes are generally used for  

    represent the multiline or 

    docstring'''   

print(str3)  

Output:

Welcome Python

Welcome Python

Triple quotes are generally used for

    represent the multiline or

    docstring

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Strings indexing 

Like other languages, the indexing of the Python strings starts from 0. For example, The string "HELLO" is indexed as given in the below figure.

s

Example: 

str = "HELLO"  

print(str[0])  

print(str[1])  

print(str[2])  

print(str[3])  

print(str[4])  

# It returns the IndexError because 6th index doesn't exist  

print(str[6])  

Output:

H

E

L

L

O

IndexError: string index out of range

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Strings Positive Index position 

Examples: 

# Given String 

str = "International" 

# Start Oth index to end 

print(str[0:]) 

# Starts 1th index to 4th index 

print(str[1:5]) 

# Starts 2nd index to 3rd index 

print(str[2:4]) 

# Starts 0th to 2nd index 

print(str[:3]) 

#Starts 4th to 6th index 

print(str[4:7])

Output:

International

nter

te

Int

Rna

Strings Negative Index position 

str = 'International' 

print(str[-1]) 

print(str[-3]) 

print(str[-2:]) 

print(str[-4:-1]) 

print(str[-7:-2]) 

# Reversing the given string 

print(str[::-1]) 

print(str[-13])

Output:

l

n

al

ona

ation

lanoitanretnI

I

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String Operators

Operator	Description
+	It is known as concatenation operator used to join the strings given either side of the operator.
*	It is known as repetition operator. It concatenates the multiple copies of the same string.
[]	It is known as slice operator. It is used to access the sub-strings of a particular string.
[:]	It is known as range slice operator. It is used to access the characters from the specified range.
in	It is known as membership operator. It returns if a particular sub-string is present in the specified string.
not in	It is also a membership operator and does the exact reverse of in. It returns true if a particular substring is not present in the specified string.
r/R	It is used to specify the raw string. Raw strings are used in the cases where we need to print the actual meaning of escape characters such as "C://python". To define any string as a raw string, the character r or R is followed by the string.
%	It is used to perform string formatting. It makes use of the format specifiers used in C programming like %d or %f to map their values in python. We will discuss how formatting is done in python.

     Examples of Operators :

str = "Hello"     

str1 = " world"    

print(str*3) # prints HelloHelloHello    

print(str+str1)# prints Hello world     

print(str[4]) # prints o                

print(str[2:4]); # prints ll                    

print('w' in str) # prints false as w is not present in str    

print('wo' not in str1) # prints false as wo is present in str1.     

print(r'C://python37') # prints C://python37 as it is written    

print("The string str : %s"%(str)) # prints The string str : Hello   

Output:

HelloHelloHello

Hello world

o

ll

False

False

C://python37

The string str : Hello

Example: 

  # using triple quotes  

print('''''They said, "What's there?"''')  

# escaping single quotes  

print('They said, "What\'s going on?"')  

# escaping double quotes  

print("They said, \"What's going on?\"")  

Output:

They said, "What's there?"

They said, "What's going on?"

They said, "What's going on?"

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Escape Sequence with Example

Sr.	Escape Sequence	Description	Example
1.	\newline	It ignores the new line.	print("Python1 \ Python2 \ Python3") Output: Python1 Python2 Python3
2.	\\	Backslash	print("\\") Output: \
3.	\'	Single Quotes	print('\'') Output: '
4.	\\''	Double Quotes	print("\"") Output: "
5.	\a	ASCII Bell	print("\a")
6.	\b	ASCII Backspace(BS)	print("Hello \b World") Output: Hello World
7.	\f	ASCII Formfeed	print("Hello \f World!") Hello  World!
8.	\n	ASCII Linefeed	print("Hello \n World!") Output: Hello  World!
9.	\r	ASCII Carriege Return(CR)	print("Hello \r World!") Output: World!
10.	\t	ASCII Horizontal Tab	print("Hello \t World!") Output: Hello    World!
11.	\v	ASCII Vertical Tab	print("Hello \v World!") Output: Hello  World!
12.	\ooo	Character with octal value	print("\110\145\154\154\157") Output: Hello
13	\xHH	Character with hex value.	print("\x48\x65\x6c\x6c\x6f") Output: Hello

other Example: 

print("C:\\Users\\Poonam Sharma\\Python32\\Lib")  

2.      print("This is the \n multiline quotes")  

3.      print("This is \x44\x45\x46 representation")

output

C:\Users\Poonam Sharma\Python32\Lib

This is the

 multiline quotes

This is HEX representation

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The format() method

The format() method is the most flexible and useful method in formatting strings. The curly braces {} are used as the placeholder in the string and replaced by the format() method argument. Let's have a look at the given example:

  # Using Curly braces  

print("{} and {} both are the best friend".format("Ramesh","Mahesh"))  

#Positional Argument  

print("{1} and {0} best players ".format("Virat","Rohit"))  

#Keyword Argument  

print("{a},{b},{c}".format(a = "James", b = "Peter", c = "Ricky"))  

Output

Ramesh and Mahesh both are the best friend

Rohit and Virat best players 

James,Peter,Ricky 

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