Python Questions and Answers - List Comprehension - 1

This set of Python Multiple Choice Questions & Answers (MCQs) focuses on “List Comprehension – 1”.

1. What will be the output of the following Python code?

l=[1,2,3,4,5]
[x&1 for x in l]

a) [1, 1, 1, 1, 1]
b) [1, 0, 1, 0, 1]
c) [1, 0, 0, 0, 0]
d) [0, 1, 0, 1, 0]
View Answer

Answer: b
Explanation: In the code shown above, each of the numbers of the list, that is, 1, 2, 3, 4 and 5 are AND-ed with 1 and the result is printed in the form of a list. Hence the output is [1, 0, 1, 0, 1].

2. What will be the output of the following Python code?

l1=[1,2,3]
l2=[4,5,6]
[x*y for x in l1 for y in l2]

a) [4, 8, 12, 5, 10, 15, 6, 12, 18]
b) [4, 10, 18]
c) [4, 5, 6, 8, 10, 12, 12, 15, 18]
d) [18, 12, 6, 15, 10, 5, 12, 8, 4]
View Answer

Answer: c
Explanation: The code shown above returns x*y, where x belongs to the list l1 and y belongs to the list l2. Therefore, the output is: [4, 5, 6, 8, 10, 12, 12, 15, 18].

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3. Write the list comprehension to pick out only negative integers from a given list ‘l’.
a) [x<0 in l]
b) [x for x<0 in l]
c) [x in l for x<0]
d) [x for x in l if x<0]
View Answer

Answer: d
Explanation: To pick out only the negative numbers from a given list ‘l’, the correct list comprehension statement would be: [x for x in l if x<0].

For example if we have a list l=[-65, 2, 7, -99, -4, 3]
>>> [x for x in l if x<0]
The output would be: [-65, -99, -4].

4. What will be the output of the following Python code?

s=["pune", "mumbai", "delhi"]
[(w.upper(), len(w)) for w in s]

a) Error
b) [‘PUNE’, 4, ‘MUMBAI’, 6, ‘DELHI’, 5]
c) [PUNE, 4, MUMBAI, 6, DELHI, 5]
d) [(‘PUNE’, 4), (‘MUMBAI’, 6), (‘DELHI’, 5)]
View Answer

Answer: d
Explanation: If we need to generate two results, we need to put it in the form of a tuple. The code shown above returns each word of list in uppercase, along with the length of the word. Hence the output of the code is: [(‘PUNE’, 4), (‘MUMBAI’, 6), (‘DELHI’, 5)].

5. What will be the output of the following Python code?

l1=[2,4,6]
l2=[-2,-4,-6]
for i in zip(l1, l2):
	print(i)

   2, -2
   4, -4
   6, -6

b) [(2, -2), (4, -4), (6, -6)]
c)

   (2, -2)
   (4, -4)
   (6, -6)

d) [-4, -16, -36]
View Answer

Answer: c
Explanation: The output of the code shown will be:
(2, -2)
(4, -4)
(6, -6)
This format is due to the statement print(i).

6. What will be the output of the following Python code?

l1=[10, 20, 30]
l2=[-10, -20, -30]
l3=[x+y for x, y in zip(l1, l2)]
print(l3)

a) Error
b) 0
c) [-20, -60, -80]
d) [0, 0, 0]
View Answer

Answer: d
Explanation: The code shown above returns x+y, for x belonging to the list l1 and y belonging to the list l2. That is, l3=[10-10, 20-20, 30-20], which is, [0, 0, 0].

7. Write a list comprehension for number and its cube for l=[1, 2, 3, 4, 5, 6, 7, 8, 9].
a) [x**3 for x in l]
b) [x^3 for x in l]
c) [x**3 in l]
d) [x^3 in l]
View Answer

Answer: a
Explanation: The list comprehension to print a list of cube of the numbers for the given list is: [x**3 for x in l].

8. What will be the output of the following Python code?

l=[[1 ,2, 3], [4, 5, 6], [7, 8, 9]]
[[row[i] for row in l] for i in range(3)]

a) Error
b) [[1, 4, 7], [2, 5, 8], [3, 6, 9]]
c)

   1 4 7
   2 5 8
   3 6 9

   (1 4 7)
   (2 5 8)
   (3 6 9)

View Answer

Answer: b
Explanation: In the code shown above, ‘3’ is the index of the list. Had we used a number greater than 3, it would result in an error. The output of this code is: [[1, 4, 7], [2, 5, 8], [3, 6, 9]].

9. What will be the output of the following Python code?

import math
[str(round(math.pi)) for i in range (1, 6)]

a) [‘3’, ‘3’, ‘3’, ‘3’, ‘3’, ‘3’]
b) [‘3.1’, ‘3.14’, ‘3.142’, ‘3.1416’, ‘3.14159’, ‘3.141582’]
c) [‘3’, ‘3’, ‘3’, ‘3’, ‘3’]
d) [‘3.1’, ‘3.14’, ‘3.142’, ‘3.1416’, ‘3.14159’]
View Answer

Answer: c
Explanation: The list comprehension shown above rounds off pi(3.141) and returns its value, that is 3. This is done 5 times. Hence the output is: [‘3’, ‘3’, ‘3’, ‘3’, ‘3’].

10. What will be the output of the following Python code?

l1=[1,2,3]
l2=[4,5,6]
l3=[7,8,9]
for x, y, z in zip(l1, l2, l3):
	print(x, y, z)

    1 4 7
    2 5 8
    3 6 9

    (1 4 7)
   (2 5 8)
   (3 6 9)

c) [(1, 4, 7), (2, 5, 8), (3, 6, 9)]
d) Error
View Answer

Answer: a
Explanation: The output of the code shown above is:
1 4 7
2 5 8
3 6 9
This is due to the statement: print(x, y,z).

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