String¶

STRING DATA TYPE¶

The most commonly used object in any project and in any programming language is String

How to define multi-line String Literals?¶

We can define multi-line String literals by using triple single or double quotes.

multi_line_str = """Any sequence of characters 
within either single quotes 
or double quotes is considered 
as a String."""
print(multi_line_str)

How to Access Characters of a String?¶

We can access characters of a string by using the following ways.

By using index
By using slice operator

1) Accessing Characters By using Index¶

Python supports both +ve and -ve Index.

name = "Ashish Bindra"

print(name[0]) # A
print(name[5]) # h
print(name[-1]) # a
print(name[20])
IndexError: string index out of range

2) Accessing Characters by using Slice Operator¶

Syntax: name bEginindex:endindex:step]
Begin Index: From where we have to consider slice (substring)
End Index: We have to terminate the slice (substring) at endindex-1
Step: Incremented Value.

str1 = "Learning Python is very very easy!!!"

print(str1[1:7:1]) # earnin
print(str1[1:7])   # earnin
print(str1[1:7:2]) # eri
print(str1[:7])    # Learnin
print(str1[7:])    # g Python is very very easy!!!
print(str1[::])    # Learning Python is very very easy!!!
print(str1[:])     # Learning Python is very very easy!!!
print(str1[::-1])  # !!!ysae yrev yrev si nohtyP gninraeL

Mathematical Operators for String¶

We can apply the following mathematical operators for Strings.

1) * operator for concatenation 2) * operator for repetition

print("Hello" + "World") # HelloWorld
print("Hi"*2)            # HiHi

Note¶

1) To use + operator for Strings, compulsory both arguments should be str type. 2) To use * operator for Strings, compulsory one argument should be str and other argument should be int.

Q) Write a Program to access each Character of String in Forward and Backward Direction by using while Loop?¶

s = "Learning Python is very easy !!!" 
n = len(s) 
i = 0 

print("Forward direction") 

while i<n: 
    print(s[i],end=' ') 
    i +=1 

print("\n\nBackward direction") 
i = -1 

while i >= -n: 
    print(s[i],end=' ') 
    i = i-1


# o/p
# Forward direction
# L e a r n i n g   P y t h o n   i s   v e r y   e a s y   ! ! ! 

# Backward direction
# ! ! !   y s a e   y r e v   s i   n o h t y P   g n i n r a e L

Alternative ways:

s = "Learning Python is very easy !!!" 

print("Forward direction") 
for i in s[::]: 
    print(i,end=' ') 

print("\nBackward direction")
for i in s[::-1]: 
    print(i,end=' ')

Checking Membership¶

We can check whether the character or string is the member of another string or not by using in and not in operators.

str1 = 'durga' 

print('d' in str1) # True
print('z' in str1) # False

str1 = input("Enter main string: ") 
subs = input("Enter sub string: ") 

if subs in str1: 
    print(f"\"{subs}\" is found in main string") 
else: 
    print(f"\"{subs}\" is not found in main string")
# Enter main string: Ashish Bindra
# Enter sub string: sh
# "sh" is found in main string

Comparison of Strings¶

We can use comparison operators (<, <=, >, >=) and equality operators (==, !=) for strings.
Comparison will be performed based on alphabetical order.

s1=input("Enter first string: ") 
s2=input("Enter Second string: ") 

if s1==s2: 
    print("Both strings are equal") 
elif s1<s2: 
    print("First String is less than Second String") 
else: 
    print("First String is greater than Second String")

o/p Enter first string: durga Enter Second string: durga Both strings are equal

Removing Spaces from the String¶

We can use the following 3 methods

1) rstrip(): To remove spaces at right hand side 2) lstrip(): To remove spaces at left hand side 3) strip(): To remove spaces both sides

city=input("Enter your city Name: ") 
scity=city.strip() 

if scity=='Hyderabad': 
    print("Hello Hyderbadi..Adab") 
elif scity=='Chennai': 
    print("Hello Madrasi...Vanakkam") 
elif scity=="Bangalore": 
    print("Hello Kannadiga...Shubhodaya") 
else: 
    print("your entered city is invalid")

# Enter your city Name:Bangalore 
# Hello Kannadiga...Shubhodaya

Finding Substrings¶

We can use the following 4 methods

For forward direction:

1) find() 2) index()

For backward direction:

1) rfind() 2) rindex()

find()¶

s.find(substring)

Returns index of first occurrence of the given substring. If it is not available then we will get -1.

s="Learning Python is very easy" 

print(s.find("Python")) #9 
print(s.find("Java")) # -1 
print(s.find("r"))#3 
print(s.rfind("r"))#21

s.find(substring,bEgin,end)¶

It will always search from bEgin index to end-1 index.

s="durgaravipavanshiva" 

print(s.find('a'))#4 
print(s.find('a',7,15))#10
print(s.find('z',7,15))#-1

index()¶

index() method is exactly same as find() method except that if the specified substring is not available then we will get ValueError.

s=input("Enter main string:") 
subs=input("Enter sub string:") 

try: 
    n=s.index(subs) 
except ValueError: 
    print("substring not found") 
else: 
    print("substring found")

o/p Enter main string:learning python is very easy Enter sub string:python substring found

Counting substring in the given String¶

We can find the number of occurrences of substring present in the given string by using count() method.

s.count(substring): It will search through out the string.
s.count(substring, bEgin, end): It will search from bEgin index to end-1 index.

s="abcabcabcabcaddab" 

print(s.count('a'))     # 6  
print(s.count('ab'))    # 5
print(s.count('abc'))   # 4
print(s.count('a',3,7)) # 2

Replacing a String with another String¶

s.replace(oldstring, newstring) inside s, every occurrence of old String will be replaced with new String.

eg 1

s = "Learning Python is very difficult"

s1 = s.replace("difficult","easy") 
print(s1) # Learning Python is very easy

Eg 2: All occurrences will be replaced

s = "ababababababab" 

replace_str = s.replace("a","b") 
print(replace_str)

Q) String Objects are Immutable then how we can change the Content by using replace() Method¶

Once we creates string object, we cannot change the content.This non changeable behaviour is nothing but immutability.
If we are trying to change the content by using any method, then with those changes a new object will be created and changes won't be happend in existing object.
Hence with replace() method also a new object got created but existing object won't be changed.

we can see new object which was created because of replace() method.

str1 = "abab" 
str2 = str1.replace("a","b") 

print(str1,"is available at :",id(str1)) 
print(str2,"is available at :",id(str2))

o/p

abab is available at : 2604224914096<br>
bbbb is available at : 2604225153904

Splitting of Strings¶

We can split the given string according to specified seperator by using split() method.
l = s.split(seperator)
The default seperator is space. The return type of split() method is List.

s="durga software solutions" 

l=s.split() 
for x in l: 
    print(x)
# o/p
# durga
# software
# solutions

date = "22-07-2024" 
date_list = date.split('-') 

for val in date_list: 
    print(val)
# o/p
# 22
# 07
# 2024

Joining of Strings¶

We can join a Group of Strings (List OR Tuple) wrt the given Seperator.

s = seperator.join(group of strings)

names = ('sunny', 'bunny', 'chinny') 
list_name = '-'.join(names) 
print(list_name) # sunny-bunny-chinny

Changing Case of a String: We can change case of a string by using the following 4 methods¶

upper(): To convert all characters to upper case
lower(): To convert all characters to lower case
swapcase(): Converts all lower case characters to upper case and all upper case characters to lower case
title(): To convert all character to title case. i.e first character in every word should be upper case and all remaining characters should be in lower case.
capitalize(): Only first character will be converted to upper case and all remaining characters can be converted to lower case
casefold(): Return a version of the string suitable for caseless comparisons.

line = 'learning Python is very Easy' 

print(line.upper())      # LEARNING PYTHON IS VERY EASY
print(line.lower())      # learning python is very easy
print(line.swapcase())   # LEARNING pYTHON IS VERY eASY
print(line.title())      # Learning Python Is Very Easy
print(line.capitalize()) # Learning python is very easy
print(line.casefold())   # learning python is very easy

Checking Starting and Ending Part of the String¶

Python contains the following methods for this purpose

s.startswith(substring)
s.endswith(substring)

line = 'learning Python is very easy' 

print(line.startswith('learning')) # True
print(line.endswith('learning'))   # False
print(line.endswith('easy'))       # True

To Check Type of Characters Present in a String: Python contains the following methods for this purpose¶

isalnum(): Returns True if all characters are alphanumeric( a to z , A to Z ,0 to9 )
isalpha(): Returns True if all characters are only alphabet symbols(a to z,A to Z)
isdigit(): Returns True if all characters are digits only( 0 to 9)
islower(): Returns True if all characters are lower case alphabet symbols
isupper(): Returns True if all characters are upper case aplhabet symbols
istitle(): Returns True if string is in title case
isspace(): Returns True if string contains only spaces

print('Durga786'.isalnum()) # True 
print('durga786'.isalpha()) # False
print('durga'.isalpha()) # True 
print('durga'.isdigit()) # False 
print('786786'.isdigit()) # True 
print('abc'.islower()) # True 
print('Abc'.islower()) # False 
print('abc123'.islower()) # True 
print('ABC'.isupper()) # True 
print('Learning python is Easy'.istitle()) # False 
print('Learning Python Is Easy'.istitle()) # True
print(' '.isspace()) # True

demo.py
s=input("Enter any character:")

if s.isalnum():
    print("Alpha Numeric Character") 
    if s.isalpha(): 
        print("Alphabet character") 
        if s.islower(): 
            print("Lower case alphabet character") 
        else:
            print("Upper case alphabet character") 
    else: 
        print("it is a digit") 
elif s.isspace():
    print("It is space character") 
elif not s.isalnum():
    print("it is a float")
else:
    print("Non Space Special Character")

Important Programs regarding String Concept¶

Q1) Write a Program to Reverse the given String¶

Input: durga
Output: agrud

1st way

str1 = input("Enter Some String: ") # ashish
print(str1[::-1]) # hsihsa

2st way

str1 = input("Enter Some String: ") # Python
print(''.join(reversed(str1))) # nohtyP

3st way

str1 = input("Enter Some String: ") # Python

i = len(str1) - 1 
target='' 

while i >= 0: 
    target = target + str1[i] 
    i = i - 1 

print(target) # nohtyP

"4st way"

4st way

s = "hello"
reversed_s = ""

for char in s:
    reversed_s = char + reversed_s

print(reversed_s)  # Output: "olleh"

"Using a List Comprehension

Using a List Comprehension

s = "hello"
reversed_s = ''.join([s[i] for i in range(len(s)-1, -1, -1)])
print(reversed_s)  # Output: "olleh"

Using Recursion

def reverse_recursive(s):
    if len(s) == 0:
        return s
    else:
        return reverse_recursive(s[1:]) + s[0]

s = "hello"
reversed_s = reverse_recursive(s)
print(reversed_s)  # Output: "olleh"

Using reduce() from functools

from functools import reduce

s = "hello"
reversed_s = reduce(lambda acc, char: char + acc, s)
print(reversed_s)  # Output: "olleh"

Q2) Program to Reverse Order of Words¶

Input: Learning Python is very Easy
Output: Easy Very is Python Learning

```py "

line=input("Enter Some String: ") # Learning Python is very Easy

list_line = line.split()
l1 = [] i = len(list_line) - 1

while i >= 0: l1.append(list_line[i]) output = ' '.join(l1) i = i - 1

print(output) # Easy very is Python Learning

```py
line=input("Enter Some String: ")  # Learning Python is very Easy

list_line = line.split()  
list_line.reverse()

print(" ".join(list_line)) # Easy very is Python Learning

Write a Program to find the Number of Occurrences of each Character present in the given String?¶

Input: ABCABCABBCDE
Output: A-3,B-4,C-3,D-1,E-1

str1 = input("Enter the Some String: ") 

d = {} 
for x in str1: 
    if x in d.keys(): 
        d[x] = d[x] + 1  
    else: 
        d[x] = 1

for k, v in d.items(): 
        print(f"{k} = {v} Times")

Enter the Some String: Ashsih
A = 1 Times
s = 2 Times
h = 2 Times
i = 1 Times

Assignment Question / Answers¶

66. Python Program to Print Output Without a Newline¶

name = "ashish"
print(name,end="")

77. Python Program to Trim Whitespace From a String¶

strip()

str1 = " Python Program  "
str1.strip()

ltrip()

str1= " Python Program "
str1.lstrip()

rtrip()

str1= "Python Program  "
str1.rstrip()

71. Python Program to Create a Long Multiline String¶

# Example 1: Using triple quotes
my_string = '''The only way to
learn to program is
by writing code.'''

print(my_string)

# Example 2: Using parentheses and a single/double quotes
my_string = ("The only way to \n"
         "learn to program is \n"
         "by writing code.")

print(my_string)

41. Python Program to Sort Words in Alphabetic Order¶

way1

# Program to sort alphabetically the words form a string provided by the user

my_str = "Hello this Is an Example With cased letters"

# To take input from the user
#my_str = input("Enter a string: ")

# breakdown the string into a list of words
words = [word.lower() for word in my_str.split()]

# sort the list
words.sort()

# display the sorted words

print("The sorted words are:")
for word in words:
   print(word)

way 2

s = "v a"
ss = s.split()
ss.sort()
ss

way2

names = "jashan himanshu ashish"
list_names = names.split(" ")

names = " ".join(sorted(list_names))

print(names)

91. Python Program to Capitalize the First Character of a String¶

s = "ashish"

s.capitalize()

67. Python Program to Check If a String Is a Number (Float)¶

way 1

def is_float(value):
    try:
        float(value)
        return True
    except ValueError:
        return False

test_string1 = "123.45"

print(f"Is '{test_string1}' a float? {is_float(test_string1)}")

way 2

type(is_float) == type(3.9)

type(is_float) == type(float())

way 3

input_str = input("Enter somthing!! ").strip()

if input_str.isalpha():
    print("you enter alphabet which is string!!")
elif input_str.isdigit():
    print("String is a int!!")
else:
    print("String is float or punctuation!!")

way 4

input_str = input("Enter somthing!! ").strip()

try:
    input_str =  eval(input_str)
    if isinstance(input_str,int):
        print("you entered int")
    elif isinstance(input_str,float):
        print("you entered float")
except (NameError,SyntaxError):
    print("this is string ")

way 5

input_str = input("Enter some string ")

try:
    input_str = eval(input_str)

    if  type(input_str) == type(int()):
        print("You entered an int")

    elif type(input_str) == type(float()):
        print("You entered a float")
except (NameError,SyntaxError):
    print("This is string ")

39. Python Program to Check Whether a String is Palindrome or Not¶

way 1

s = "madam"

"palindrome" if ''.join(reversed(s)) == s else "not palindrome"

way 2

s= "level"

if s==s[::-1]: 
    print('The given string is palindrome') 
else: 
    print('The given string is not palindrome')

way 3

# Program to check if a string is palindrome or not

my_str = 'aIbohPhoBiA'

# make it suitable for caseless comparison
my_str = my_str.casefold()

# reverse the string
rev_str = reversed(my_str)

# check if the string is equal to its reverse
if list(my_str) == list(rev_str):
   print("The string is a palindrome.")
else:
   print("The string is not a palindrome.")

way 4

my_str = 'aIbohPhoBiA'.lower()
rev_str = ""

for s in my_str:
    rev_str=s + rev_str
print(my_str,id(my_str))
print(rev_str,id(rev_str))

if rev_str == my_str:
    print("The string is a palindrome.")
else: 
    print("The string is not a palindrome.")

way 5

my_str = 'pabap'.lower()

if len(my_str)==1 :
    print("The string is a palindrome.")
else:
    for i in range(0,len(my_str)//2):
        if my_str[i] != my_str[-1-i]:
            print("The string not is a palindrome.",my_str[-1-i])
            break    
    else:
         print("The string is a palindrome.")

40. Python Program to Remove Punctuations From a String¶

# define punctuation
punctuations = '''!()-[]{};:'"\,<>./?@#$%^&*_~'''

my_str = "Hello!!!, he said ---and went."

# To take input from the user
# my_str = input("Enter a string: ")

# remove punctuation from the string
no_punct = ""
for char in my_str:
   if char not in punctuations:
       no_punct = no_punct + char

# display the unpunctuated string
print(no_punct)

Using str.translate() with string.punctuation

import string

def remove_punctuation(text):
    return text.translate(str.maketrans('', '', string.punctuation))

# Example usage
text = "Hello, World! How's everything?"
cleaned_text = remove_punctuation(text)
print(cleaned_text)  # Output: Hello World Hows everything

Using str.replace()

def remove_punctuation(text):
    punctuations = '''!()-[]{};:'"\,<>./?@#$%^&*_~'''
    for char in punctuations:
        text = text.replace(char, "")
    return text

# Example usage
text = "Hello, World! How's everything?"
print(remove_punctuation(text))

Using Regular Expressions

import re

def remove_punctuation(text):
    return re.sub(r'[^\w\s]', '', text)

# Example usage
text = "Hello, World! How's everything?"
print(remove_punctuation(text))

43. Python Program to Count the Number of Each Vowel¶

way-1

s = "ashish Bindru"
v="aeiou" 

for w in v:
    print(s.count(w))
# print("The different vowel present in",w,"are",d)

way-2

w = "ashish Bindru"

s=set(w) 

v={'a','e','i','o','u'} 
d=s.intersection(v) 

print("The different vowel present in",w,"are",d)

way-3

vowels = { "a":0, "e":0, "i":0, "o":0, "u":0 }
s = "ashish Bindru"

vowels = {word: s.count(word) for word in 'aeiou'}
print(vowels)

way-4

vowels = { "a":0, "e":0, "i":0, "o":0, "u":0 }

s = "ashish Bindru"

vowels =  {word:s.count(word) for word in s if word in vowels}

print(vowels)

way-5

vowels = { "a":0, "e":0, "i":0, "o":0, "u":0 }

s = "ashish Bindru"

for word in s:
    if word in vowels:
        vowels[word]+=1

print(vowels)

way-6

# Program to count the number of each vowels

# string of vowels
vowels = 'aeiou'

ip_str = 'Hello, have you tried our tutorial section yet?'

# make it suitable for caseless comparisions
ip_str = ip_str.casefold()

# make a dictionary with each vowel a key and value 0
count = {}.fromkeys(vowels,0)

# count the vowels
for char in ip_str:
   if char in count:
       count[char] += 1

print(count)

way-7

# Using a list and a dictionary comprehension
# Using dictionary and list comprehension

ip_str = 'Hello, have you tried our tutorial section yet?'

# make it suitable for caseless comparisions
ip_str = ip_str.casefold()

# count the vowels
count = {x:sum([1 for char in ip_str if char == x]) for x in 'aeiou'}

print(count)

47. Python Program to Create Pyramid Patterns¶

way-1

n=7
for i in range(1,n+1):
    print(" "*(n-i),end="")

    for j in range(1,i+1):
        print("*",end=" ")

    print()

way-2

k = 0
rows = 7
for i in range(1, rows+1):
    for space in range(1, (rows-i)+1):
        print(end="  ")

    while k!=(2*i-1):
        print("* ", end="")
        k += 1

    k = 0
    print()

61. Python Program to Parse a String to a Float or Int¶

Example 1: Parse string into integer

balance_str = "1500"
balance_int = int(balance_str)

# print the type
print(type(balance_int))

# print the value
print(balance_int)

Example 2: Parse string into float

balance_str = "1500.4"
balance_float = float(balance_str)

# print the type
print(type(balance_float))

# print the value
print(balance_float)

Example 3: A string float numeral into integer

balance_str = "1500.34"
balance_int = int(float(balance_str))

# print the type
print(type(balance_int))

# print the value
print(balance_int)

63. Python Program to Convert String to Datetime¶

from datetime import datetime

my_date_string = "Mar 11 2011 11:31AM"

datetime_object = datetime.strptime(my_date_string, '%b %d %Y %I:%M%p')

print(type(datetime_object))
print(datetime_object)

from dateutil import parser

date_time = parser.parse("Mar 11 2011 11:31AM")

print(date_time)
print(type(date_time))

65. Python Program to Get a Substring of a String¶

# Using String slicing
my_string = "I love python."

# prints "love"
print(my_string[2:6])

# prints "love python."
print(my_string[2:])

# prints "I love python"
print(my_string[:-1])

my_string.find("love")

my_string.index("love")

68. Python Program to Count the Occurrence of an Item in a List¶

way-1

numbers = [1, 2, 3, 2, 4, 2, 5]
item = 2
count = 0

for element in numbers:
    if element == item:
        count += 1

print(f"{element_to_count} occurs {count} times in the list.")

way-2

numbers = [1, 2, 3, 2, 4, 2, 5]

count_num = set(numbers)

for n in count_num:
    if numbers.count(n):
        print(f"{n} occures {numbers.count(n)}")

way-3

numbers = [1, 2, 3, 2, 4, 2, 5]

l1 = []
l2 = []
for num in numbers:
    if num not in l1:
        l1.append(num)
    else:
        l2.append(num)


l1,l2

way-4

from collections import Counter

my_list = [1, 2, 3, 4, 2, 2, 5, 6, 5, 3]

occurrences = Counter(my_list)
occurrences

way-5

# Using count() method
freq = ['a', 1, 'a', 4, 3, 2, 'a'].count('a')
print(freq)

87. Python Program to Reverse a Number¶

way-1

n = 12345
str(n)[::-1]

way-2

n = 12345343

new =0
while n:
    r =n%10
    new = new * 10 +r
    n = n//10
new

way-3

n = 12345

s =''.join(reversed(str(n)))
s

90. Python Program to Check If Two Strings are Anagram¶

Two strings are said to be anagrams iff both are having same content irrespective of characters position.

way-1

s1 = "papa"
s2 = "appa"

if sorted(s1) == sorted(s2):
    print("The strings are anagrams.")
else:
    print("The strings aren't anagrams.")

way-2

s1 = "".join(sorted(s1))
s2 = "".join(sorted(s2))

if s1 is s2:
    print("The strings are anagrams.")
else:
    print("The strings aren't anagrams.") 
print(s1,s2)

way-3

from collections import Counter

# Function to check if two strings are anagrams
def are_anagrams(str1, str2):
    # Anagrams must have the same length
    if len(str1) != len(str2):
        return False
    print(Counter(str1))
    # Compare character counts using Counter
    return Counter(str1) == Counter(str2)
are_anagrams("lazy","zaly")

92. Python Program to Compute all the Permutation of the String¶

Permutation is the method of selecting elements from a set in different ways.

For example: the number of ways in which characters from yup can be selected are

yup, ypu, uyp, upy, puy, pyu, and not selecting any

way-1

def get_permutation(string, i=0):

    if i == len(string):     
        print("".join(string))

    for j in range(i, len(string)):

        words = [c for c in string]

        # swap
        words[i], words[j] = words[j], words[i]

        get_permutation(words, i + 1)

print(get_permutation('yup'))

way-2

for p in permutations('pro'):
    print(p)

way-3

from itertools import permutations

words = [''.join(p) for p in permutations('pro')]

print(words)

94. Python Program to Count the Number of Occurrence of a Character in String¶

way-1

count = 0 

my_string = "ashish bindra"
my_char = "r"

for i in my_string:
    if i == my_char:
        count += 1

print(count)

way-2

print(my_string.count(my_char))

way-3

s = "ashish bindra"
d={}

for x in s: 
    if x in d.keys(): 
        d[x]=d[x]+1 
    else: 
        d[x]=1

for k,v in d.items():
    print(f"{k} = {v} Times")

96. Python Program to Convert Bytes to a String¶

byte_data = b'Hello, World!'
print(type(byte_data))

string_data = byte_data.decode('utf-8')
print(type(string_data))

value = bytes("ashish".encode())

print(value, type(value))