Class 12 Computer Science Python Revision Tour – II Notes
String/Text Handling in Python
What is a String?
Python strings are characters enclosed in quotes of any type – single quotation marks, double quotation marks, triple quotation marks.
An Empty string is a string that has 0 characters, i.e. ‘ ’ , “ ”, “““ ”””
S = ‘Anjeev Singh Academy’ ,
T = “Singh@123”
Example:-
Mline = ‘‘‘Anjeev Singh Academy
is the best free online academy
on YouTube ’’’
Characteristics of String
Python strings is an immutable data type, i.e. not allowed to change in place. S[0] =‘R’ not allowed
Strings are sequences of characters, where each character has a unique index number.
The indexes of strings begin from 0 to length-1, in forward direction and -1, -2, -3, …. , -length in backward direction.

String Traversal
Traversing a String or Text means accessing all characters of the string, character by character, through its index position.
Program – 1 : Python program to traverse a string forward using Loop.
Name = "mycstutorial.in"
for ch in Name:
print(ch, end= " ")
Output:
m y c s t u t o r i a l . i n
Program 2 – Python program to traverse a string forward using indexing.
Name = "mycstutorial.in"
for index in range(len(Name)):
print(Name[index], end= " ")
Output:
m y c s t u t o r i a l . i n
Program 3 – Python program to traverse a string backward using indexing.
Name = "mycstutorial.in"
for index in range(len(Name)-1, -1, -1):
print(Name[index], end= " ")
Output:
n i . l a i r o t u t s c y m
Program 4 – Python program to search a character in the string using indexing.
Name = "mycstutorial.in"
ch = input("Enter a character to search : ")
Found = False
for index in range(len(Name)-1, -1, -1):
if Name[index] == ch:
Found = True
if Found :
print(ch, "found in", Name)
else:
print(ch, "not found")
Output:
Enter a character to search : o
o found in mycstutorial.in
Enter a character to search : x
x not found
Program 5 – Python program to count occurrences of a character in the string using indexing.
Name = "abc abc xyz abc pqr"
ch = input("Enter a character to count : ")
count = 0
for index in range(len(Name)-1, -1, -1):
if Name[index] == ch:
count += 1
print(ch, "found ", count, "time(s)")
Output:
Enter a character to search : a
a found 3 time(s)
Enter a character to search : p
p found 1 time(s)
Enter a character to search : t
t found 0 time(s)
String Operators
Strings can be manipulated by using string operators. Python supports the following types of string operators.
Operator | Name | Description |
+ | Concatenation | Add two strings i.e. concatenate two strings. e.g. S = “Hello” + “Shyam” |
* | Replication / Repetition | Replicate the string upto n times. |
in / not in | Membership | To check given character exists in the string or not. |
[index] | Element Accessor | Extract the character from the given index position. |
[ : ] | Slicing [start:end:step] | Extracts the characters from the given range i.e start to stop |
==, !=, < , > , <=, >= | Relational / Comparison Operator | These relational operators can do comparison between strings, based on character by character comparison rules for Unicode or Ordinal Value |
String Slicing
Slice means ‘a part of’. In Python, a string slice refers to a part of the string containing some contiguous characters from the string.
Syntax:
string[start : end : step]
- where start and end are integers with legal indices.
- will return the characters falling between indices start and end. i.e. start, start+1, start+2,…, till end-1.
- By default value of step is 1. It is an optional argument.
Example: –
Slice | Output, if str = “Hello Anjeev” |
str[ 2 : ] | ‘llo Anjeev” |
str[ : 5] | “Hello” |
str[4 : 8] | “o Anj” |
str[ : : 2] | “HloAje” |
str[ : : -1] | “veejnA olleH” |
str[-6 : -2 ] | “Anje” |
String Functions
Syntax to call the method – string.methodName( )
Methods | Description |
isalpha() | Returns True, if the string contains only letters, otherwise returns False. >>>”abc”.isalpha() True >>>”1abc”.isalpha() False |
isalnum() | Returns True, if the string contains alphanumeric (i.e. alphabets or number or both), otherwise returns False. >>>”abc”.isalnum() True >>>”123″.isalnum() True >>>”a123″.isalnum() True >>>”@#2″.isalnum() False >>>”@#12ab”.isalnum() False |
isdigit( ) | Return True, if the string contains only digits, otherwise returns False. >>>”123″.isdigit() True >>>”abc123″.isdigit() False |
isspace( ) | Returns True, if the string contains only spaces, otherwise returns False. >>>” “.isspace() True >>>”a “.isspace() False >>>” a”.isspace() False |
islower( ) | Returns True if the string contains all lowercase characters, otherwise returns False. >>>”mycstutorial.in”.islower() True >>>”MYCSTUTORIAL.IN”.islower() False |
isupper() | Returns True, if the string contains all uppercase characters, otherwise returns False. >>>”MYCSTUTORIAL.IN”.isupper() True >>>”mycstutorial.in”.isupper() False |
istitle( ) | Returns True, if string is properly “TitleCasedString”, otherwise returns False. >>>”Anjeev Singh Academy”.istitle() True >>>”Anjeev singh academy”.istitle() False >>>”Anjeevsinghacademy”.istitle() True |
startswith() | Returns True, if string is starts with the given substring. >>> name=”tanmay singh” >>> name.startswith(‘tan’) True >>> name.startswith(‘tannu’) False |
endswith() | Returns Ture, if string is ends with the given substring. >>> name=”tanmay singh” >>> name.endswith(‘singh’) True >>> name.endswith(‘nh’) False |
Methods | Description |
len(string ) | Returns the length of string, i.e. number of characters. >>> name=”tanmay singh” >>> len(name) 12 |
capitalize( ) | Returns a copy of string with its first character capitalized. >>> name=”tanmay singh” >>> name.capitalize() ‘Tanmay singh’ |
lower( ) | Returns a copy of string converted to lowercase. >>> name=”TANMAY SINGH” >>> name.lower() ‘tanmay singh’ |
upper( ) | Returns a copy of string converted to uppercase. >>> name=”tanmay singh” >>> name.upper() ‘TANMAY SINGH’ |
title() | Returns a copy of string converted to title case. >>> name=”tanmay singh” >>> name.title() ‘Tanmay Singh’ |
swapcase() | Converts and returns all uppercase characters to lowercase and vice-versa. >>> name=”Tanmay Singh” >>> name.swapcase() ‘tANMAY sINGH’ |
index(char) | Search and returns the first occurence of given character or substring. >>> name=”tanmay singh” >>> name.index(‘y’) 5 |
ord(char) | Returns the ordinal value (ASCII) of given character. >>> ord(‘a’) 97 >>> ord(‘A’) 65 >>> ord(‘#’) 35 |
chr(num) | Returns character represented by inputted ASCII number. >>> chr(35) ‘#’ >>> chr(65) ‘A’ >>> chr(97) ‘a’ |
Methods | Description |
count() | Returns the number of times a specified value occurs in a string. >>> name=”tanmay singh” >>> name.count(‘a’) 2 |
lstrip() / lstrip(char) | Returns a copy of the string with leading characters removed. By default removed space. >>> data = ‘ hello ‘ >>> data.lstrip() ‘hello ‘ >>> mesg = ‘aaaRAMaaa’ >>> mesg.lstrip(‘a’) ‘RAMaaa’ |
rstrip()/ rstrip(char) | Returns a copy of the string with trailing characters removed. By default removed space. >>> data = ‘ hello ‘ >>> data.rstrip() ‘ hello’ >>> mesg = ‘aaaRAMaaa’ >>> mesg.rstrip(‘a’) ‘aaaRAM’ |
strip() | Returns a copy of the string with leading and trailing characters removed. >>> data = ‘ hello ‘ >>> data.strip() ‘hello’ >>> mesg = ‘aaaRAMaaa’ >>> mesg.strip(‘a’) ‘RAM’ |
split() | Splits the string at the specified separator, and returns a list. >>> name=”tanmay singh” >>> name.split(‘n’) [‘ta’, ‘may si’, ‘gh’] >>> message = “Hello dear welcome to mycstutorial.in” >>> message.split() [‘Hello’, ‘dear’, ‘welcome’, ‘to’, ‘mycstutorial.in’] |
partition() | Splits the string at the specified separator, and returns a tuple. >>> name=”tanmay singh” >>> name.partition(‘n’) (‘ta’, ‘n’, ‘may singh’) >>> message = “Hello dear welcome to mycstutorial.in” >>> message.partition(‘ ‘) (‘Hello’, ‘ ‘, ‘dear welcome to mycstutorial.in’) |
join() | Returns a string in which the string elements have been joined by a string separator. Eg. ‘-’.join(‘anjeev” => ‘a-n-j-e-e-v’ >>> name=”tanmay singh” >>> ‘#’.join(name) ‘t#a#n#m#a#y# #s#i#n#g#h’ >>> “–He–“.join(name) ‘t–He–a–He–n–He–m–He–a–He–y–He– –He–s–He–i–He–n–He–g–He–h’ |
Class 12 Computer Science Python Revision Tour – II Notes