Hackerrank Collections and Data Structures 5

Question 1

Which collection type is best suited for implementing a thread-safe FIFO queue in Python?

Accepted Answer

collections.deque

Answer

deque's append() and popleft() operations are atomic in CPython, making it safe for use as a FIFO queue in single-producer single-consumer scenarios.

Question 2

What does `Counter & Counter` (intersection) compute?

Accepted Answer

Minimum counts (keeps only shared elements with min count)

Answer

Counter intersection keeps elements present in both counters, taking the minimum count for each.

Question 3

Which attribute of a `namedtuple` class holds default values for fields (Python 3.6.1+)?

Accepted Answer

_field_defaults

Answer

`_field_defaults` is a dict mapping field names to their default values defined at class creation.

Question 4

How does `collections.defaultdict` differ from `dict.setdefault()`?

Accepted Answer

defaultdict inserts on read access; setdefault only inserts if explicitly called

Answer

defaultdict automatically inserts the default value when a missing key is accessed; setdefault must be called explicitly and only inserts once per call.

Question 5

What is the output of: `from collections import deque; d = deque([1,2,3], maxlen=3); d.append(4); print(list(d))`?

Accepted Answer

[2, 3, 4]

Answer

With maxlen=3, appending a 4th element discards the oldest element (1) from the left, leaving [2, 3, 4].

(Hackerrank) HackerRank Python Certification Practice Test

(Hackerrank) HackerRank Python Certification Practice Test

Hackerrank Collections and Data Structures 5