lower()	Returns the exact copy of the string with all the letters in lowercase.	>>> str1='SAVE EARTH' >>> print(str1.lower())            save eath
islower()	Returns True if the string is in lowercase.	>>> str1='welcome' >>> print (str1.islower())            True

nhy re teloW

(i) Learn
(ii) r
(iii) er
(iv) ceoenyo

strl ="COMPUTER"
index = 0
for i in strl:
print (strl [:index+ 1])
index+=I

(i) T
(ii) THIRU
(iii) THIRU
(iv) KURAL

(i) Once you define a string, python allocate an index value for its each character.
(ii) These index values are otherwise called as subscript which are used to access and manipulate the strings. The subscript can be positive or negative integer numbers.

(i) Slice is a substring of a main string. A substring can be taken from the original string by using [ ]. operator and index or subscript values. 
(ii) Thus, [ ] is also known as slicing operator.Using slice operator, you have to slice one or more substrings from a main string.
General format of slice operation :
Str [start : end]

Output : School School School

Python will not allow deleting a particular character in a string. Whereas you can remove entire string variable using del command.
Example :
>>> strl="How about you"
>>> print (str1)
        How about you
>>> del str1
>>> print (str1)
Traceback (most recent call last):
         File "", line 1, in
                 print (strl)
NameError : name 'str1' is not defined

(i) String is a data type in python, which is used to handle array of characters.
(ii) 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.
(iii) Example :
Welcome to learning Python"
"Welcome to learning Python"
""Welcome to learning Python""

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) 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) 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:

String	S	C	H	O	O	L
Positive subscript	0	1	2	3	4	5
Built in functions	-6	-5	-4	-3	-2	-1

Syntax	Description	Example
count (str,beg,end)	Returns the number of substrings Occurs within the given range. Remember that substring may be a single character. Range (beg and end) arguments are optional. If it is not given, python searched in whole string. Search is case sensitive.	>>>str1="Raja Raja Chozhan" >>>print(str1.count("Raja")) 2 >>>print(str1.count("r")) 0 >>>print(str1.count("R")) 2 >>>print(str1.count("a")) 5 >>>print(str1.count('a',0,5)) 2 >>>print(str1.count('a',11)) 1

 

(i) The format( ) function used with strings is very versatile and powerful function used for formatting strings.
(ii) The curly braces {} are used as placeholders or replacement fields which get replaced along with format( ) function.
Example:
num1 = int (input("Number 1:")) 
num2 = int (input("Number 2:")) 
print ("The, sum of {} and {} is {}". format (num1, num2, (num1 + num2)))
Output:
Number 1: 34
Number 2: 54
The sum of 34 and 54 is 88.

Output:
Weool

Str 1 = "COMPUTER"
index = 0
for i in str 1:
print (str 1[:index -1])
index =1

str1=input ("Enter a string:")
str2="aAeEiloOuU"
v,c=0,0
for i in str1:
if i in str2:
v+=1
else:
c+=1
print ("The given string contains {} vowels and {} consonants".format(v.c))
Output:
Enter a string: Tamilnadu School Education.
The given string contains 11 vowels and 15 consonants.

strl=' * '
i=1
while i< = 5:
print (strl*i)
i+=1

str1 = input ("Enter a string:")
str2 ="
index=-1
for i in str1:
str2 += str1[index]
index -=1
print ("'The given string = {} \n The Reversed string = {}".format(str1, str2))
if (str1==str2):
print ("Hence, the given string is Palindrome")
else:
print ("Hence, the given is not a palindrome")
Output:1
Enter a string: malayalam
The given string = malayalam
The Reversed string = malayalam
Hence, the given string is Palindrome
Output: 2
Enter a string: welcome
The given string = welcome
The Reversed string = emoclew
Hence, the given string is not a palindrome

String Operators:
Python provides the following operators for string operations. These operators are useful to manipulate string.
(i) Concatenation (+):
Joining of two or more strings is called as Concatenation. The plus (+) operator is used to concatenate strings in python.
Example:
>>> "welcome" + "Python"
'welcome python'
(ii) Append (+ =):
Adding more strings at the end of an existing string is known as append. The operator += is used to append a new string with an existing string.
Example:
>>> str1 = "welcome to"
>>> str1 + = "Learn Python"
>>> print (str1)
Welcome to Learn Python
(iii) Repeating (*):
The multiplication operator (*) is used to display a string in multiple number of times.
Example:
>>> str1= "welcome "
>>> print (str1 *4)
Welcome Welcome Welcome Welcome
(iv) String slicing:
Slice is a substring of a main string.
A substring can be taken from the original string by using [ ] operator and index or subscript values. Thus [ ] is also known as slicing operator. Using slice operator, we have to slice one or more substrings from a main string.
General format of slice operation:
str[start:end]
Where start is the beginning index and end is the last index value of a character in the string. Python takes the end value less than one from the actual index specified.
Example: I
Slice a single character from a string
>>>str 1 = "THIRUKKURAL"
>>>print (str 1 [0])
       T
(v) Stride when slicing string:

• When the slicing operator, we can specify a third argument as the stride, which refers to the number of characters to move forward after the first character is retrieved from the string.
• The default  value of stride is 1
• Python takes the last value as n-1
• We can also use negative value stride, to print data in reverse order.

Example :
>>>str1 = "Welcome to learn python"
>>>print(str1[::-2])
Output :
nhy re teolW