Class 12 CS Chapter 2 Python Revision Tour II Solutions — PYTHON TUTORIAL 2021

Python Revision Tour II Solutions

Class 12 CS Chapter 2 Python Revision Tour II Solutions

Q 1. What is indexing in context to Python strings ? Why is it also called two-way indexing ?

Ans. In Python strings, each individual character is given a location number, called index and this process is called indexing.
Python allocates indices in two direction :

• in forward direction, the indexes are numbered as 0, 1, 2,…. length-1
• in backward direction, the indexes are numbered as -1, -2. -3…. length.
  This is known as two-way indexing.

Q 2. What is a string slice ? How is it useful ?

Ans. A sub-part or a slice of a string, say s, can be obtained using s[n:m] where n and m are integers. Python returns all the character at indices n, n+1, n+2…m-1 e.g.,
‘Well done’ [1:4] will give ‘ell’

Q 3. Figure out the problem with following code fragment. Correct the code and then print the output.

1. s1 = 'must' 2. s2 = 'try' 3. n1 = 10 4. n2 = 3 5. print(s1+s2) 6. print(s2*n2) 7. print(s1+n1) 8. print(s2*s1)

Ans. The problem is wih lines 7 and 8.

This problem can be solved either by changing the operator or operand e.g., all the following statements will work :

(a) print(s1*n1) (b) print(s1+str(n1)) (c) print(s1+s2)

Line 8 — print(s2*s1) will cause error because two strings cannot be used for replication. The corrected statement will be :

Q 4. Consider the following code : [Python Revision Tour II]

string = input("Enter a string") count = 3 while True : if string[0] == 'a' : string = string[2:] elif string[-1] == 'b' : string = string[:2] else : count += 1 break print(string) print(count)

What will be the output produced, if the input is :

Ans.

(a) bbcc (b) cc (c) cc 4 4 4

Q 5. Consider the following code :

Inp = input("Please enter a string :") while len(Inp) <= 4 : if Inp[-1] == 'z' : #condition 1 Inp = Inp[0:3] + 'c' elif 'a' in Inp : #condition 2 Inp = Inp[0] + 'bb' elif not int(Inp[0]) : #condition 3 Inp = '1' + Inp[1:] + 'z; else : Inp = Inp + '*' print(Inp)

What will be the output produced if the input is (i) 1bzz, (ii) ‘1a’ (iii) ‘abc’ (iv) ‘0xy’, (v) ‘xyz’.

Ans.
(i) 1bzc*
(ii) 1bb**
(iii) endless loop because ‘a’ will always remain in index 0 and condition 3 will be repeated endlessly.
(iv) 1Xyc*
(v) Raises an error as Inp[0] cannot be converted to int.

Q 6. Write a program that takes a string with multiple words and then capitalizes the first letter of each word and forms a new string out of it. (Python Revision Tour II)

string = input("Enter a string :") length = len(string) a = 0 end = length string2 = ' ' #empty string while a<length : if a == 0 : string2 += string[0].upper( ) a += 1 elif (string[a] == ' ' and string[a+1] != ' ') : string2 += string[a] string2 += string[a+1].upper( ) a += 2 else : string2 += string[a] a += 1 print("Original String :", string) print("Captilized words String :", string2)

Q 7. Write a program that reads a string and checks whether it is a palindrome string or not.

sting = input("Enter a string :") length = len(string) mid = length/2 rev = -1 for a in range(mid) : if string[a] == string[rev] : a += 1 rev -+ 1 else : print(string, "is not a palindrome") break else : #loop else print(string, "is a palindrome")

Q 8. How are lists different from strings when both are sequences ?

Ans. The lists and strings are different in following ways :

(i) The lists are mutable sequences while strings are immutable.
(ii) In consecutive locations, a string stores the individual characters while a list stores the references of its elements.
(iii) String store single type of elements — all characters while lists can store elements belonging to different types.

Q 9. What are nested lists ?

Ans. When a list is contained in another list as a member-element, it is called nested list, e.g.,

The above list a has three elements — an integer 2, an integer 3 and a list [4, 5], hence it is nested list.

Q 10. What is output produced by the following code snippet ?

aLst = [1, 2, 3, 4, 5, 6, 7, 8, 9] print(aLst[::3])

Ans.

Q 11. What will be the output of the following code snippet ?

Lst = [1, 2, 3, 4, 5, 6, 7, 8, 9] Lst[::2] = 10, 20, 30, 40, 50, 60 print(Lst)

(a) ValueError : attempt to assign sequence of size 6 to extended slice of size 5
(b) [10, 2, 20, 4, 30, 6, 40, 8, 50, 60]
© [1, 2, 10, 30, 40, 50, 60]
(d) [1, 10, 3, 20, 5, 30, 7, 40, 9, 50, 60]

Ans. (a)

Q 12 What will be the output of the following code ?

values = [ ] for i in range (1, 4) : values.append(i) print(values)

Ans.

Q 13. What will be the output of the following code ?

rec = {"Name" : "Python", "Age" : "20"} r = rec.copy( ) print(id(r) == id(rec))

(a) True (b) False © 0 (d) 1

Ans. (b)

Q 14. What will be the output of the following code snippet ?

dc1 = {} dc1[1] = 1 dc1['1'] = 2 dc1[1.0] = 4 sum = 0 for k in dc1 : sum += dc1[k] print(sum)

Ans.

Q 15. Predict the output of following code fragment :

fruit = {} f1 = ['Apple', 'Banana', 'apple', 'Banana'] for index in f1 : if index in fruit : fruit[index] += 1 else : fruit[index] = 1 print(fruit) print(len(fruit))

Ans.

{'Apple' : 1} {'Apple' : 1, 'Banana' : 1} {'Apple' : 1, 'Banana' : 1, 'apple' : 1} {'Apple' : 1, 'Banana' : 2, 'apple' : 1} 3

Q 16. Find the error in following code. State the reason of the error.

aLst = {'a' : 1, 'b' : 2, 'c' : 3} print(aLst['a', 'b'])

Ans. The above code will produce KeyError, the reason being that there is no key same as the list [‘a’, ‘b’] in dictionary aLst.
It seems that the above code intends to print the values of two keys ‘a’ and ‘b’, thus we can modify the above code to perform this as :

aLst = {'a' : 1, 'b' : 2, 'c' : 3} print(aLst['a'], aLst['b'])

Now it will give the result as :

Q 17. Find the error in the following code fragment. State the reason behind the error.

box = { } jars = { } crates = { } box['biscuit'] = 1 box['cake'] = 3 jars['jam'] = 4 crates['box'] = box crates['jars'] = jars print[crates[box])

Ans. The above code will produce error with print( 0 because it is trying to print the value from dictionary crates by specify a key which is of a mutable type dictionary(box is a dictionary). There can never be a key of mutable type in a dictionary, hence the error.
The above code can be corrected by changing the print( ) as :

print(crates['box'])

Q 18. Write the most appropriate list method to perform the following tasks.

(a) Delete a given element from the list.
(b) Delete 3rd element from the list.
© Add an element in the end of the list.
(d) Add an element in the beginning of the list.
(e) Add elements of a list in the end of a list.

Q 19. How are tuples different from lists when both are sequences ?
Ans. The tuples and lists are different in following ways :

• The tuples are immutable sequences while lists are mutable.
• List can grow or shrink while tuples cannot.

Q 20. How can you say that a tuple is an ordered list of objects ?

Ans. A tuple is an ordered list of objects. This is evidenced by the fact that the objects can be accessed through the use of an ordinal index and for a given index, same element is returned everytime.

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