Python Revision Tour II

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
Lists and tuples are similar sequence types in python, but they are distinct data types. Both are used to store collections of items, but they have different properties and use cases. Lists are mutable, meaning you can add, remove, or modify elements after the list is created. Tuples, on the other hand, are immutable, meaning once a tuple is created, its contents cannot be changed.

(b)

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Explanation
In Python, strings are immutable, meaning once they are created, their contents cannot be changed. Whenever we modify a string, python creates a new string object to hold the modified contents, leaving the original string unchanged. On the other hand, lists in python are mutable, meaning we can modify their contents after they have been created. When we modify a list, python does not create a new list object. Instead, it modifies the existing list object in place. Strings are sequences of characters, and each character in a string can be accessed by its index. Lists, on the other hand, can store any type of data, including integers, floats, strings.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
In Python, strings are immutable, meaning once they are created, their contents cannot be changed. Whenever we modify a string, python creates a new string object to hold the modified contents, leaving the original string unchanged. On the other hand, lists in python are mutable, meaning we can modify their contents after they have been created. When we modify a list, python does not create a new list object. Instead, it modifies the existing list object in place.

(d)

Assertion is false but Reason is true.

Explanation
Dictionaries are indexed by keys and each key must be immutable and unique. However, the dictionary itself is mutable, meaning that we can add, remove, or modify key-value pairs within the dictionary without changing the identity of the dictionary object itself. Mutability refers to the ability to change a value in place without creating a new storage location for the changed value.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
A dictionary is a unordered set of key : value pairs and are indexed by keys. The values of a dictionary can change but keys of dictionary cannot be changed because through them data is hashed. Hence dictionaries are mutable but keys are immutable and unique.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
Insertion sort is a sorting algorithm that builds a sorted list, one element at a time from the unsorted list by inserting the element at its correct position in sorted list. In Insertion sort, each successive element is picked and inserted at an appropriate position in the previously sorted array.

index

Reason — The index is the numbered position of a letter in the string.

in

Reason — in is membership operator which returns True if a character or a substring exists in the given string else returns False.

immutable

Reason — Dictionaries are indexed by keys and its keys must be of any immutable type.

he

Reason — str[:2] here slicing operation begins from index 0 and ends at index 1. Hence the output will be 'he'.

list

Reason — A list can store a sequence of values belonging to any data type and they are depicted through square brackets.

tuple

Reason — For creating a tuple, enclosing the elements inside parentheses is optional. Even if parentheses are omitted as shown here, still this statement will create a tuple.

dictionary

Reason — Dictionaries are mutable with elements in the form of a key:value pair that associate keys to values.

(6.0, 27.0)

Reason — The value of expression is in round brackets because it is tuple.
3 + 3.00 = 6.0
3**3.0 = 3 x 3 x 3 = 27.0

del AL[2]
AL[2:3] = []
AL.remove(3)

Reason — del AL[2] — The del keyword deletes the element from the list AL from index 2.
AL[2:3] = [] — The slicing of the list AL[2:3] begins at index 2 and ends at index 2. Therefore, the element at index 2 will be replaced by an empty list [].
AL.remove(3) — The remove() function removes an element from the list AL from index 3."

'This is a string'
"This is a string"

Reason — Strings are enclosed within single or double quotes.

mywork

Reason — The + operator creates a new string by joining the two operand strings.

myWORK

Reason — string.upper() method returns a copy of the string converted to uppercase. The + operator creates a new string by joining the two operand strings.

'1' + 2

Reason — The + operator has to have both operands of the same type either of number type (for addition) or of string type (for concatenation). It cannot work with one operand as string and one as a number.

34

Reason — The + operator concatenates two strings and int converts it to integer type.

int("3" + "4")
= int("34")
= 34

Line 4

Reason — Index 5 is out of range because list has 5 elements which counts to index 4.

Day = {1:'Monday', 2:'Tuesday', 3:'wednesday'}

Reason — The syntax of dictionary declaration is:

<dictionary-name> = {<key>:<value>, <key>:<value>}

According this syntax, Day = {1:'Monday', 2:'Tuesday', 3:'wednesday'} is the correct answer.

list

Reason — A list can store a sequence of values belonging to any data type and enclosed in square brackets.

T[2] = -29

Reason — Tuples are immutable. Hence we cannot perform item-assignment in tuples.

False

Reason — Lists are ordered sequences. In the above two lists, even though the elements are same, they are at different indexes (i.e., different order). Hence, they are two different lists.

False

Reason — A list can store any data types and even list can contain another list as element.

True

Reason — The list can be of any size.

False

Reason — A list is a standard data type of python that can store a sequence of values belonging to any data type.

True

Reason — List can have duplicate values.

True

Reason — Dictionaries are indexed by keys. Hence its keys must be of any non-mutable type.

False

Reason — The + operator has to have both operands of the same type either of number type (for addition) or both of string type (for concatenation). It cannot work with one operand as string and one as a number.

True

Reason — The clear() method removes all items from the dictionary and the dictionary becomes empty dictionary post this method. del statement removes the complete dictionary as an object.

True

Reason — Tuples should contain same type of elements for max() and min() method to work.

False

Reason — In Python, a list of characters and a string type are not similar. Strings are immutable sequences of characters, while lists are mutable sequences that can contain various data types. Lists have specific methods and behaviors that differ from strings, such as append(), extend(), pop() etc.

True

Reason — s[:n] — The slicing of a string starts from index 0 and ends at index n-1.
s[n:] — The slicing of a string starts from index n and continues until the end of the string.
So when we concatenate these two substrings we get original string s.

False

Reason — The keys of a dictionary must be of immutable types.

Strings in python are stored as individual characters in contiguous memory locations, with two-way index for each location. The index (also called subscript) is the numbered position of a letter in the string. Indices begin 0 onwards in the forward direction up to length-1 and -1,-2, .... up to -length in the backward direction. This is called two-way indexing.

name = input("Enter name:")
for i in range(0, len(name), 2):
    print(name[i:i+2])

Enter name:python
py
th
on

A list is a standard data type of python that can store a sequence of values belonging to any type. Lists are mutable i.e., we can change elements of a list in place. Their dynamic nature allows for flexible manipulation, including appending, inserting, removing, and slicing elements. Lists offer significant utility in data storage, iteration, and manipulation tasks.

Mutability means that the value of an object can be updated by directly changing the contents of the memory location where the object is stored. There is no need to create another copy of the object in a new memory location with the updated values. Examples of mutable objects in python include lists, dictionaries.
In python, "in place" tasks refer to operations that modify an object directly without creating a new object or allocating additional memory. For example, list methods like append(), extend(), and pop() perform operations in place, modifying the original list, while string methods like replace() do not modify the original string in place but instead create a new string with the desired changes.

listA = [8, 9, 10]

1. listA[1] = 17
2. listA.extend([4, 5, 6])
3. listA.pop(0)
4. listA.sort()
5. listA = listA * 2
6. listA.insert(3, 25)

a[x:y] returns a slice of the sequence from index x to y - 1. So, a[1 : 1] will return an empty list irrespective of whether the list has two elements or less as a slice from index 1 to index 0 is an invalid range.

The two methods to add something to a list are:

1. append method — The syntax of append method is list.append(item).

2. extend method — The syntax of extend method is list.extend(<list>).

Difference

The difference between the append() and extend() methods in python is that append() adds one element at the end of a list, while extend() can add multiple elements, given in the form of a list, to a list.

Example

append method:

lst1 = [10, 12, 14]    
lst1.append(16)  
print(lst1)  

Output — [10, 12, 14, 16]

extend method:

t1 = ['a', 'b', 'c']  
t2 = ['d', 'e']  
t1.extend(t2)  
print(t1)  

Output — ['a', 'b', 'c', 'd', 'e']

The two ways to remove something from a list are:

1. pop method — The syntax of pop method is List.pop(<index>).

2. del statement — The syntax of del statement is

del list[<index>] # to remove element at index
del list[<start>:<stop>] # to remove elements in list slice

Difference

The difference between the pop() and del is that pop() method is used to remove single item from the list, not list slices whereas del statement is used to remove an individual item, or to remove all items identified by a slice.

Example

pop() method:

t1 = ['k', 'a', 'e', 'i', 'p', 'q', 'u']  
ele1 = t1.pop(0)
print(ele1)

Output — 'k'

del statement:

lst = [1, 2, 3, 4, 5]
del lst[2:4]
print(lst)

Output — [1, 2, 5]

1. states = []
2. states.append('Delhi')
3. states.append('Punjab')
4. states2 = ['Rajasthan', 'Gujarat', 'Kerala']
5. states2.insert(0,'Odisha')
6. states2.insert(2,'Tripura')
7. a = states2.index('Gujarat')
   states2.insert(a - 1,'Haryana')
8. b = states2.pop(4)
   print(b)

Tuples are used to store multiple items in a single variable. It is a collection which is ordered and immutable i.e., the elements of the tuple can't be changed in place. Tuples are useful when values to be stored are constant and need to be accessed quickly.

A dictionary is termed as an unordered collection of objects because the elements in a dictionary are not stored in any particular order. Unlike string, list and tuple, a dictionary is not a sequence. For a dictionary, the printed order of elements is not the same as the order in which the elements are stored.

Keys of a dictionary must be of immutable types such as

1. a Python string
2. a number
3. a tuple (containing only immutable entries)

For a tuple to be used as a key in a dictionary, all its elements must be immutable as well. If a tuple contains mutable elements, such as lists, sets, or other dictionaries, it cannot be used as a key in a dictionary.

Yes, we can modify the contents of a dictionary.
Values of key-value pairs are modifiable in dictionary. New key-value pairs can also be added to an existing dictionary and existing key-value pairs can be removed.
However, the keys of the dictionary cannot be changed. Instead we can add a new key : value pair with the desired key and delete the previous one.
For example:

d = { 1 : 1 }
d[2] = 2   
print(d)
d[1] = 3   
print(d)
d[3] = 2
print(d)
del d[2]
print(d)

{1: 1, 2: 2}  
{1: 3, 2: 2} 
{1: 3, 2: 2, 3: 2}  
{1: 3, 3: 2} 

d is a dictionary which contains one key-value pair.
d[2] = 2 adds new key-value pair to d.
d[1] = 3 modifies value of key 1 from 1 to 3.
d[3] = 2 adds new key-value pair to d.
del d[2] deletes the key 2 and its corresponding value.

del D deletes the entire dictionary D. After executing del D, the variable D is no longer defined, and any attempt to access D will result in a NameError.
del D[<key>] deletes the key-value pair associated with the specified key from the dictionary D. After executing del D[<key>], the dictionary D still exists, but the specified key and its corresponding value are removed from the dictionary.

For example:

d = {1: 'a' , 2 : 'b'} 
del d[2] 
print(d)
del d
print(d)

{1:'a'}
NameError: name 'd' is not defined.

1. In this example, the dictionary D does not contain the key 'd'. Therefore, attempting to access this key by D['d'] results in a KeyError because the key does not exist in the dictionary.
2. If we try to assign a value to a nonexistent key in a dictionary, python will create that key-value pair in the dictionary. In this example, the key 'd' did not previously exist in the dictionary D. When we attempted to assign the value 'spam' to the key 'd', python created a new key-value pair 'd': 'spam' in the dictionary D.

D = {'a' : 1, 'b' : 2, 'c' : 3}
D['d'] = 'spam'

D = {'a' : 1, 'b' : 2, 'c' : 3, 'd' : 'spam'}

Sorting refers to arranging elements of a sequence in a specific order — ascending or descending.

Sorting Techniques are as follows :

1. Bubble Sort
2. Insertion Sort
3. Selection Sort
4. Heap Sort
5. Quick Sort

Bubble Sort :
In Bubble sort, the adjoining values are compared and exchanged if they are not in proper order. This process is repeated until the entire array is sorted.

Insertion Sort :
Insertion sort is a sorting algorithm that builds a sorted list one element at a time from the unsorted list by inserting the element at its correct position in sorted list.

hellohellohello 123
10 helloworld

str(123) converts the number 123 to string and stores in y so y becomes "123". "hello" * 3 repeats "hello" 3 times and stores it in x so x becomes "hellohellohello".

"hello" + "world" concatenates both the strings so x becomes "helloworld". As "helloworld" contains 10 characters so len(x) returns 10.

h : e : l : l : o : t : o :   : P : y : t : h : o : n : w : o : r : l : d :

The code concatenates three strings "hello", "to Python", and "world" into the variable x. Then, it iterates over each character in x using a for loop. For each character, it assigns it to the variable y and prints y followed by a colon and space, all on the same line due to the end=" " parameter.

he hello wor ld
w ll
llo wo or

print(x[:2], x[:-2], x[-2:]) —
x[:2] extracts the substring from the beginning of x up to index 1, resulting in "he".
x[:-2] extracts the substring from the beginning of x up to the third last character, resulting in "hello wor".
x[-2:] extracts the substring from the last two characters of x until the end, resulting in "ld".
Hence, output of this line becomes he hello wor ld

print(x[6], x[2:4]) —
x[6] retrieves the character at index 6, which is 'w'.
x[2:4] extracts the substring from index 2 up to index 3, resulting in "ll".
Hence, output of this line becomes w ll

print(x[2:-3], x[-4:-2]) —
x[2:-3] extracts the substring from index 2 up to the fourth last character, resulting in "llo wo".
x[-4:-2] extracts the substring from the fourth last character to the third last character, resulting in "or".
Hence, output of this line becomes llo wo or

word_list = eval(input("Enter a list of words: "))
total_length = 0
for word in word_list:
    total_length += len(word)
average_length = total_length / len(word_list)
print("Average length of words:", average_length)

Enter a list of words: ["apple", "banana", "orange", "kiwi"] 
Average length of words: 5.25

1. The code prompts the user to enter a list of words and assigns it to the variable word_list.
2. We iterate over word_list using for loop. Inside the loop, length of each word gets added to total_length variable.
3. Average length is calculated by dividing total_length by the number of words in word_list.

[4, 3, 2]

The slicing notation a[start:stop:step] extracts a portion of the list from index start to stop-1 with a specified step. In the slicing part a[3:0:-1]:

• start is 3, which corresponds to the element with value 4.
• stop is 0, but as element at stop index is excluded so slicing goes up to index 1.
• step is -1, indicating that we want to step backward through the list.

Putting it together:

a[3:0:-1]

This extracts elements from index 3 to (0+1) in reverse order with a step of -1.

The output of the code will be:

[4, 3, 2]

234566

1. arr is initialised as a list with elements [1, 2, 3, 4, 5, 6].
2. for loop iterates over the indices from 1 to 5. For each index i, it assigns the value of arr[i] to arr[i - 1], effectively shifting each element one position to the left. After this loop, the list arr becomes [2, 3, 4, 5, 6, 6].
3. Second for loop iterates over the indices from 0 to 5 and prints each element of the list arr without newline characters because of end="" parameter. Then it prints the elements of the modified list arr, resulting in 234566.

1 # 
1 # 2 # 
1 # 2 # 3 # 

1. Numbers is a list containing the numbers 9, 18, 27, and 36.
2. The outer for loop iterates over each element in the list Numbers.
3. The inner loop iterates over the range from 1 to the remainder of Num divided by 8. For example, if Num is 9, the range will be from 1 to 1 (9 % 8 = 1). If Num is 18, the range will be from 1 to 2 (18 % 8 = 2), and so on. Then it prints the value of N, followed by a "#", and ensures that the output is printed on the same line by setting end=" ".
4. After both loops, it prints an empty line, effectively adding a newline character to the output.

t[0] = 6 will raise a TypeError as tuples are immutable (i.e., their elements cannot be changed after creation).

There are no errors in this python code. Lists in python can contain elements of any type. As lists are mutable so t[0] = 6 is also valid.

t[4] = 6 will raise an error as we are trying to change the value at index 4 but it is outside the current range of the list t. As t has 3 elements so its indexes are 0, 1, 2 only.

t[0] = "H" will raise an error because strings in python are immutable, meaning we cannot change individual characters in a string after it has been created. Therefore, attempting to assign a new value to t[0] will result in an error.

The errors in this code are:

1. In the list [Amar, Shveta, Parag], each element should be enclosed in quotes because they are strings.
2. The equality comparison operator is '==' instead of = for checking equality.
3. if statement should be lowercase.

There are two issue in range(len(words), 0, -1):

1. The start index len(words) is invalid for the list words as it will have indexes from 0 to len(words) - 1.
2. The end index being 0 means that the last element of the list is missed as the list will be iterated till index 1 only.

The corrected python code is :

for i in range(len(words)-1, -1, -1):
    print(words[i], end=' ')

a is: Hello
b is: Nita
c is: How's
d is: life ?
Hi Nita

ntpl is a tuple containing 4 elements. The statement (a, b, c, d) = ntpl unpacks the tuple ntpl into the variables a, b, c, d. After that, the values of the variables are printed.

The statement ntpl = (a, b, c, d) forms a tuple with values of variables a, b, c, d and assigns it to ntpl. As these variables were not modified, so effectively ntpl still contains the same values as in the first statement.

ntpl[0] ⇒ "Hello"
∴ ntpl[0][0] ⇒ "H"

ntpl[1] ⇒ "Nita"
∴ ntpl[1][1] ⇒"i"

ntpl[0][0] and ntpl[1][1] concatenates to form "Hi". Thus ntpl[0][0]+ntpl[1][1], ntpl[1] will return "Hi Nita ".

True

Tuples can be declared with or without parentheses (parentheses are optional). Here, tuple_a is declared without parentheses where as tuple_b is declared with parentheses but both are identical. As both the tuples contain same values so the equality operator ( == ) returns true.

True

In the given python code snippet, id1 and id2 will point to two different objects in memory as del rec deleted the original dictionary whose id is stored in id1 and created a new dictionary with the same contents storing its id in id2. However, id1 == id2 will compare the contents of the two dictionaries pointed to by id1 and id2. As contents of both the dictionaries are same hence it returns True. If in this code we add another line print(id1 is id2) then this line will print False as id1 and id2 point to two different dictionary objects in memory.

dict_items([('name', 'Aman'), ('age', 27), ('address', 'Delhi')])

A dictionary my_dict with two key-value pairs, 'name': 'Aman' and 'age': 26 is initialized. Then updates the value associated with the key 'age' to 27. Then adds a new key-value pair 'address': 'Delhi' to the dictionary my_dict. The items() method returns all of the items in the dictionary as a sequence of (key, value) tuples. In this case, it will print [('name', 'Aman'), ('age', 27), ('address', 'Delhi')].

def display(my_list):
    for item in my_list:
        if item.isdigit():
            print(item * 3)
        else:
            print(item + '#')
display(my_list = eval(input("Enter the list :")))

Enter the elements of the list separated by spaces:41 DROND GIRIRAJ 13 ZARA
414141
DROND#
GIRIRAJ#
131313
ZARA#

1. The code prompts the user to enter the elements of the list separated by spaces and stores the input as a single string in the variable my_list.
2. Then splits the input string my_list into individual elements and stores them in a new list called new_list.
3. Then for loop iterates over each element in the new_list.
4. The isdigit() method is used to check if all characters in the string are digits. If it's true (i.e., if the element consists only of digits), then it prints the element concatenated with itself three times. Otherwise, if the element contains non-digit characters, it prints the element concatenated with the character '#'.

(i) isupper() method is used to check if a string contains only uppercase letters.

(ii) len() gives the total length of the list.

30
{(1, 2, 4): 8, (4, 2, 1): 10, (1, 2): 12}

1. An empty dictionary named my_dict is initialized.
2. my_dict[(1,2,4)] = 8, my_dict[(4,2,1)] = 10, my_dict[(1,2)] = 12 these lines assign values to the dictionary my_dict with keys as tuples. Since tuples are immutable, so they can be used as keys in the dictionary.
3. The for loop iterates over the keys of the dictionary my_dict. Inside the loop, the value associated with each key k is added to the variable sum.
4. sum and my_dict are printed.