Collections and Data Structures Flashcards

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

Answer: collections.deque

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.

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

Answer: Minimum counts (keeps only shared elements with min count)

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

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

Answer: _field_defaults

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

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

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

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

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

Answer: [2, 3, 4]

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

Which statement about `collections.OrderedDict.popitem()` is true in Python 3.7+?

Answer: It accepts last=True/False to pop from either end

OrderedDict.popitem(last=True) removes the last inserted item; passing last=False removes the first inserted item.

What does `namedtuple._make(iterable)` do?

Answer: Creates a named tuple instance from an iterable

`_make()` is a classmethod that creates a new named tuple instance from any iterable, equivalent to unpacking.