Hackerrank Iterators and Generators

Question 1

What is the output of the following code?

python
def count_up(n):
    for i in range(n):
        yield i

g = count_up(3)
print(next(g))
print(next(g))

Accepted Answer

0
1

Answer

0
0

Answer

1
2

Answer

0
1
2

Question 2

Which of the following correctly implements the iterator protocol on a custom class?

Accepted Answer

Define __iter__ returning self and __next__ returning the next value

Answer

Define __iter__ returning self and __yield__ returning the next value

Answer

Define only __next__ returning the next value

Answer

Define __iter__ returning a list of values

Question 3

What happens when a generator function reaches the end of its body without a yield?

Accepted Answer

StopIteration is raised automatically

Answer

The generator returns None repeatedly

Answer

A RuntimeError is raised

Answer

The generator restarts from the beginning

Question 4

What is the difference between these two expressions?

A: [x**2 for x in range(1000)]
B: (x**2 for x in range(1000))

Accepted Answer

A builds the full list in memory; B is a lazy generator that yields one value at a time

Answer

Both build lists but B is faster

Answer

A is a tuple comprehension; B is a generator

Answer

They are identical in behavior and memory use

Question 5

What does the built-in iter() function do when called on a list?

Accepted Answer

Returns a list_iterator object that supports __next__

Answer

Returns a copy of the list

Answer

Converts the list to a generator function

Answer

Raises TypeError because lists are not iterable

Question 6

What does the following generator produce?

python
def infinite_evens():
    n = 0
    while True:
        yield n
        n += 2

g = infinite_evens()
print([next(g) for _ in range(4)])

Accepted Answer

[0, 2, 4, 6]

Answer

[2, 4, 6, 8]

Answer

[0, 2, 4]

Answer

An infinite loop with no output