Data Structures: Dictionaries and Sets Flashcards

What does `set.issubset()` return when called as `{1, 2}.issubset({1, 2, 3})`?

Answer: True

`issubset()` returns True if every element of the calling set is also in the argument set.

What is the output of `d = {'a': [1, 2]}; e = d.copy(); e['a'].append(3); print(d['a'])`?

Answer: [1, 2, 3]

`dict.copy()` performs a shallow copy, so the list value is shared between `d` and `e`; mutating it through `e` also affects `d`.

Which method removes ALL elements from a set without deleting the set object?

Answer: .clear()

`set.clear()` removes all elements in place, leaving an empty set object.

What is the output of `{x**2 for x in range(4)}`?

Answer: {0, 1, 4, 9}

Curly braces with a single expression (no colon) and a `for` clause create a set comprehension.

What does `{1, 2, 3}.isdisjoint({4, 5, 6})` return?

Answer: True

`isdisjoint()` returns True when two sets share no common elements.

What is the output of `d = dict(a=1, b=2); print('b' in d)`?

Answer: True

The `in` operator checks for key membership in a dictionary and returns True because 'b' is a key.

What does `Counter({'a': 3, 'b': 1}) + Counter({'a': 1, 'b': 2})` produce from `collections`?

Answer: Counter({'a': 4, 'b': 3})

Adding two Counters sums the counts for each key, resulting in Counter({'a': 4, 'b': 3}).