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

count_up is a generator function. Each call to next() resumes execution until the next yield. The first next(g) yields 0; the second yields 1. Only two values are printed.

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

The iterator protocol requires __iter__ (returns the iterator object, typically self) and __next__ (returns the next value or raises StopIteration). __yield__ is not a dunder method.

Question 3

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

Accepted Answer

StopIteration is raised automatically

Answer

When a generator function's body is exhausted (no more yield statements), Python automatically raises StopIteration, signalling to a for-loop or next() caller that iteration is complete.

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

Square brackets produce a list comprehension, computing and storing all 1000 values immediately. Parentheses produce a generator expression, computing each value on demand without storing the whole sequence.

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

iter(obj) calls obj.__iter__() and returns the resulting iterator. For a list, it returns a list_iterator object. The list itself is iterable, but not an iterator — calling next() on the list directly would fail.

(Hackerrank) HackerRank Python Certification Practice Test

(Hackerrank) HackerRank Python Certification Practice Test

Hackerrank Iterators and Generators