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Python Unit-2 Answered-1

String

What is a string? Discuss the different ways of representing a string in Python.

Answer :

A string is a sequence of characters, enclosed in either single quotes (') or double quotes ("), or triple quotes (''' or """) for multi-line strings.

# single quotes
s1 = 'Hello'

# Double quotes
s2 = "World"

#Triple quotes (for multi-line strings): 
s3 = '''Hello
World
with three lines'''
# String concatenation
full_string = "Hello" + " " + "World"  
# Hello World
What do you mean by mutable and immutable data structures? Explain with examples.

Answer :

Mutable Data Structures: can be modified or changed after creation. In Python, lists, dictionaries, and sets are mutable. This means we can change, add, or remove elements from these data structures without creating a new object.

lst = [1, 2, 3]
lst[0] = 4  # Modify an element
lst.append(5)  # Add an element
print(lst)  # Output: [4, 2, 3, 5]

Immutable Data Structures: cannot be changed after they are created. In Python, tuples and strings are immutable. Once created, they cannot be modified or changed. Changes will create a new object.

tup = (1, 2, 3)
tup[0] = 4  
# TypeError: 'tuple' object does not support item assignment
str1 = "hello"
str1[0] = "H"  
# TypeError: 'str' object does not support item assignment
Demonstrate slicing on strings. Also explain the use of join() and split() string methods with examples.
  • Explain the use of join() and split() string methods with examples. What does it mean strings are immutable? Explain with an example.

Answer :

Slicing allows us to extract a portion of a string.

s = "Hello, World!"
print(s[0:5])  # Output: Hello
print(s[7:])   # Output: World!
print(s[:5])   # Output: Hello
print(s[-1])   # Output: !

join(): Combines elements of an iterable (list, tuple) into a single string, using the string as a separator. join is an string method, called upon string, so the elements in the list to be joined also have to be strings.

words = ["Python", "is", "fun"]
result = " ".join(words)

print(result)  
# Python is fun

split(): Divides a string into a list of substrings based on a delimiter.

Splitting by Space (default) :

sentence = "Python is fun"
words = sentence.split()  

print(words)  
# ['Python', 'is', 'fun']

Splitting by specified delimiter :

sentence = "apple,orange,banana"
fruits = sentence.split(",")  
# Splits by comma

print(fruits)  
# ['apple', 'orange', 'banana']
Develop a python program to find whether the given string is palindrome or not.

Answer :

Logic is to reverse the string and compare if it is equal to original string. ( Program already in Unit 1 answers)

if s == s[::-1]:
    print("Palindrome")
else:
    print("Not palindrome")
Slicing Questions

Assume that the name t is assigned a value ‘Programming with Python’ what will be the output when we execute the following commands and explain.

t[13:], t[:9], t[:], t[7:16], t[5:-10], t[6:-6:], t[-2::-1], t[::-2], t[-2:1:-2], t[:-8]

Answer :

>>> t = "Programming with Python"

>>> t[13:]
'ith Python'
>>> t[:9]
'Programmi'
>>> t[:]
'Programming with Python'
>>> t[7:16]
'ming with'
>>> t[5:-10]
'amming w'
>>> t[6:-6 : ]
'mming with '
>>> t[-2::-1]
'ohtyP htiw gnimmargorP'
>>> t[::-2]
'nhy twgimroP'
>>> t[-2:1:-2]
'otPhi nmag'
>>> t[:-8]
'Programming wit'

Assume that the name a is assigned a value ‘mca@rit’ what will be the output when we execute the following commands and explain.

a[5:], t[:4], t[2:-2:2], t[3:4], t[2:-2], t[1:-2:], t[-3::-2], t[::-4], t[-4:1:-4], t[:-3]

Answer :

>>> s = "mca@rit"

>>> s[5:]
'it'
>>> s[:4]
'mca@'
>>> s[2:-2:2]
'ar'
>>> s[3:4]
'@'
>>> s[2:-2]
'a@r'
>>> s[1:-2:]
'ca@r'
>>> s[-3::-2]
'ram'
>>> s[::-4]
'ta'
>>> s[-4:1:-4]
'@'
>>> s[:-3]
'mca@'
Program to write third person singular form verb

The third person singular verb form in English is distinguished by the suffix -s, which is added to the stem of the infinitive form: run -> runs. A simple set of rules can be given as follows:

  • If the verb ends in y, remove it and add ies
  • If the verb ends in o, ch, s, sh, x or z, add es
  • By default just add s Develop a Python Script for the rules above

Answer :

Logic is to check the last letters using endswith() method and since string is immutable, the value is changed by taking slice to remove last letter and concatenating with the plural letters according to what it ends with.

def third_person_singular(verb):
    if verb.endswith('y'):
        return verb[:-1] + 'ies'
    elif verb.endswith(('o', 'ch', 's', 'sh', 'x', 'z')):
        return verb + 'es'
    else:
        return verb + 's'


print(third_person_singular("go"))     # Output: goes
print(third_person_singular("brush"))  # Output: brushes
print(third_person_singular("fly"))    # Output: flies
Predict the output of the following and justify your answer:
i)
S="Vishweswaraiah"
print(s[4:])
print(s[:5])

weswaraiah  
# from index 4 to end

Vishw   
# from start, to 4th, excluding 5th
ii)
str1 = "Bangalore"
str1[1] = "e"
str1[6] = str1[8] = "u"
print(str1)

# TypeError: 'str' does not support assignment
iii)
a = -45
print(--a)

# output: -45
# Double negation gets same value
iv) a, b, c = True, False, False
if a or b and c:
	print "MSRIT"
else:
	print "RNSIT"

# output: MSRIT

The condition a or b and c is evaluated according to precedence of operators as True or (False and False), which will evaluate to True.

Hence, the if condition is True and MSRIT gets printed.

Write a python program to count number of vowels and consonants, identify numbers, uppercase letters, lowercase letters and special characters in a given string.
  • Write a python function that accepts a sentence containing alpha numeric characters and calculates the number of digits, uppercase and lowercase letters. Return the calculated values.

Answer :

Logic would be:

  • A character can be a special character (not a number or letter) then it will not be lower upper vowel consonant ( so can be in if else block)
  • If it is not a special character then it can be a Number so can check that next.
  • If it is not a Number or special character, then it is a
def analyze_string(input_string):
    vowels = "aeiouAEIOU"
    vowel_count = 0
    consonant_count = 0
    number_count = 0
    uppercase_count = 0
    lowercase_count = 0
    special_char_count = 0
    
    
    for char in input_string:
        # if not a alnum it is special character
        if ( not char.isalnum() ):
            special_char_count += 1
        # character is a number
        elif char.isdigit():
            number_count += 1
        # character is uppercase
        elif char.isupper():
            uppercase_count += 1
        # character is lowercase
        elif char.islower():
            lowercase_count += 1
    
# Seperate conditional for vowels, consonents  
        if char in vowels:
            vowel_count += 1
        # letter but not a vowel, so consonent
        elif char.isalpha():
            consonant_count += 1

Another Logic

  • Check if it is a alnum(), if true, check if it is a isdigit(), if false then check for vowels and upper.
  • If not alnum then it will be a special character.
def analyze_string(input_string):
    vowels = "aeiouAEIOU"
    vowel_count = 0
    consonant_count = 0
    number_count = 0
    uppercase_count = 0
    lowercase_count = 0
    special_char_count = 0
    
    for char in input_string:
        if char.isalnum():
            if char.isdigit():
                number_count += 1
            else:
                if char in vowels:
                    vowel_count += 1
                else:
                    consonant_count += 1

                if char.isupper():
                    uppercase_count += 1
                elif char.islower():
                    lowercase_count += 1
        else:
            special_char_count += 1

Additional String Practice Programs

Alternating letters to uppercase
>>> s = "hello this is python"
>>> r = ''
>>> 
>>> for i in range(0, len(s)):
...     if i % 2 == 0:
...         r = r + s[i]
...     else:
...         r = r + s[i].upper()
... 
>>> r
'hElLo tHiS Is pYtHoN'
Find the biggest word(s) in a string
str_in = input("Enter a string : ")
lis = str_in.split() # get words in list
biggest = lis[0] # consider first word
x = len(biggest) # len of first word

for i in range(1, len(lis)):
    word = lis[i]
    if len(word) > x:  # change if anything else is larger
        biggest = word
        x = len(biggest)
    elif len(word) == x: # if same length word
        biggest = f"{biggest}, {word}"

print("The biggest word(s) is/are:", biggest)

Same thing with usage of list to store multiple values when length is same.

inputStr = input("Enter a string: ")
wordList = inputStr.split()
multipleMaxWordList = []  
# List to store more than one maximum length words

maxLenWord = ''  # String to store maximum length word

for i in wordList:
    if len(i) > len(maxLenWord):
        maxLenWord = i
        multipleMaxWordList = [maxLenWord]  
        # Store only the maxWord in the list
    elif len(i) == len(maxLenWord):
        maxLenWord = i
        multipleMaxWordList.append(i)  
        # Keep adding all occurrences of maxWords in the list

print(multipleMaxWordList)

Tuples

List and describe any five methods on tuples.
  • List and describe any five functions to operate Tuples.

Answer :

Although tuples are immutable and cannot be modified, there are few methods:

  • len() : Returns the number of elements in the tuple.
  • count(x) : Returns the number of occurrences of the element x in the tuple.
  • index(x) : Returns the index of the first occurrence of element x in the tuple. Raises a ValueError if x is not found.
  • max() and min() : Returns the largest and smallest element in the tuple. The elements must be comparable.
my_tuple = (1, 2, 3, 2, 1, 2)

print(len(my_tuple))  # Output: 6

print(my_tuple.count(2)) # Output: 3

print(my_tuple.index(3)) # Output: 2

print( max(my_tuple))  # Output: 3

print( min(my_tuple))  # Output: 1

Tuple creation and unpacking

my_tuple = 1, 2, 3, 4, 5  # Parentheses are optional
print(my_tuple)  
# Output: (1, 2, 3, 4, 5)


# Unpacking a tuple
t = (1, 2, 3, 4)
a, b, c, d = t 
print(a, b, c, d)  
# Output: 1 2 3 4
Implement a program that prompts the user to enter a tuple of integers. Calculate and print the sum of all integers in the tuple.

Answer :

def sum_of_tuple():
    user_input = input("Enter tuple of integers (e.g., (1, 2, 3)): ")
    
	# Use eval to safely convert the input string to a tuple
	user_tuple = eval(user_input)
	
	total = sum(user_tuple)
    print(f"The sum of all integers in the tuple is: {total}")
    
sum_of_tuple()
Develop Python script that takes a list of words and returns the length of the longest one using tuples.

Answer :

def longest_word(words):
    word_lengths = []
    
    for word in words:
        word_lengths.append((word, len(word)))
    
    longest = word_lengths[0]
    # assuming first value is longest
    
    for word, length in word_lengths:
        if length > longest[1]:
            longest = (word, length)
            
    return longest_word[1]

words = ["apple", "banana", "grapefruit", "kiwi", "mango"]

print(f"The length of the longest word is: {longest_word(words)}")

# The length of the longest word is: 10
Program to store and convert student marks to a tuple

Write a Python program that:

  • Prompts the user to enter the number of students.
  • For each student, prompts the user to enter their marks in three subjects (e.g., Mathematics, Science, English).
  • Stores the marks of each student in a list.
  • Convert the list to a tuple.

Answer :

n = int(input("Enter the number of students: "))
t = []
for i in range(n):
    m1 = input("Enter marks for subject 1: ")
    m2 = input("Enter marks for subject 2: ")
    m3 = input("Enter marks for subject 3: ")
    t.append((m1, m2, m3))
    print()

print("Marks as tuple:", tuple(t))
Store the following data in a list, a tuple, and a dictionary:
India 91
USA   1
UK    41
Japan 9

Answer :

# List of tuples
data_list = [("India", 91), ("USA", 1), ("UK", 41), ("Japan", 9)]
# Tuple of tuples
data_tuple = (("India", 91), ("USA", 1), ("UK", 41), ("Japan", 9))
# Dictionary
data_dict = {"India": 91, "USA": 1, "UK": 41, "Japan": 9}
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