String is a data type in python, which is used to handle array of characters. String is a sequence of Unicode characters that may be a combination of letters, numbers or special symbols enclosed within single, double or even triple quotes.
Example:
'Welcome to learning python'
"Welcome to learning python"
""Welcome to learning python""
In Python, strings are immutable, it means once we define a string, it cannot be changed during execution.
Creating Strings:
A string in Python can be created using single or double or even triple quotes. String in single quotes cannot hold any other single quoted character in it, because the compiler will not recognize where to start and end the string. To overcome this problem, we have to use double quotes. Strings which contains double quotes should be define within triple quotes. Defining strings within triple quotes also allows creation of multiline strings.

Membership Operators:
(i) The 'in' and 'not in' operators can be used with strings to determine whether a string is present in another string. Therefore, these operators are called as Membership Operators.
(ii) Example:
str1=input ("Enter a string:")
str2="chennai"
if str2 in str1:
print ("Found")
else:
print ("Not Found")
(iii) Output:1
Enter a string: Chennai GHSS, Saidapet
Found
(iv) Output:2
Enter a string: Govt GHSS, Ashok Nagar Not Found

(i) 2
(ii) 2
(iii) 0
(iv) 5
(v) 2
(vi) 1

(i) python
(ii) false
(iii) false
(iv) PYTHON

(i) False
(ii) False
(iii) False

(i) 0
(ii) 3
(iii) -1
(iv) 3

(i) 11
(ii) School
(iii) * * * * Welcome * * * *

(i) carriage return
(ii) character with octal value
(iii) vertical tab

(i) % e or % E
(ii) % f
(iii) % g or % G

(i) %u
(ii) octal integer
(iii) %c or %x
(iv) signed decimal integer.

(i) character
(ii) Signed decimal integer
(iii) String

Syntax:
("String to be display with %vall and %vaI2" %(val1, vaI2))
Example:
name = "Rajarajan''
mark = 98
print ("Name: %s and Marks: %d" %(name,mark) )
Output:
Name: Rajarajan and Marks: 98

str1 = input ("Enter a string:")
Index=-1
while index >= -(lentstrl1)):
print ("Subscript[",index,"] :" + str1 [index])
index +=-1
Output:
Enter a string: welcome
Subscript [ -1 ] : e
Subscript [ -2 ] : m
Subscript [ -3 ] : 0
Subscript [ -4 ] : c
Subscript [ -5 ] : I
Subscript [ -6 ] : e
Subscript [ -7 ] : w

The positive subscript 0 is assigned to the first character and n-1 to the last character, where n is the number of charaters in the string. The negative index assigned from the last character to the first character in reverse order begins with -1.
Example: