Hackerrank Comprehensions (List, Dict, Set, and Generator Expressions)

Question 1

What does the following list comprehension produce?

python
[x**2 for x in range(5) if x % 2 == 0]

Accepted Answer

[0, 4, 16]

Answer

[0, 1, 4, 9, 16]

Answer

[4, 16]

Answer

[0, 4, 8, 16]

Question 2

Which of the following creates a dictionary mapping each word to its length from a list?

python
words = ['cat', 'elephant', 'ox']

Accepted Answer

{w: len(w) for w in words}

Answer

{len(w): w for w in words}

Answer

[w: len(w) for w in words]

Answer

{w, len(w) for w in words}

Question 3

What is the type and value of the following expression?

python
result = (x*2 for x in range(3))

Accepted Answer

A generator object yielding 0, 2, 4

Answer

The list [0, 2, 4]

Answer

The tuple (0, 2, 4)

Answer

A set {0, 2, 4}

Question 4

What does the following set comprehension produce?

python
{len(w) for w in ['hi', 'bye', 'no', 'yes']}

Accepted Answer

{2, 3}

Answer

{2, 3, 2, 3}

Answer

[2, 3, 2, 3]

Answer

{2, 2, 3, 3}

Question 5

How do you flatten a 2D list [[1,2],[3,4],[5,6]] into [1,2,3,4,5,6] using a list comprehension?

Accepted Answer

[x for row in [[1,2],[3,4],[5,6]] for x in row]

Answer

[x for x in row for row in [[1,2],[3,4],[5,6]]]

Answer

[[x for x in row] for row in [[1,2],[3,4],[5,6]]]

Answer

[row for x in [[1,2],[3,4],[5,6]] for row in x]

Question 6

Which comprehension correctly inverts a dictionary {'a':1, 'b':2, 'c':3} so values become keys?

Accepted Answer

{v: k for k, v in {'a':1,'b':2,'c':3}.items()}

Answer

{k: v for v, k in {'a':1,'b':2,'c':3}.items()}

Answer

[v, k for k, v in {'a':1,'b':2,'c':3}.items()]

Answer

{v for k, v in {'a':1,'b':2,'c':3}.items()}