Python Data Structures: Dictionaries and Sets Questions and Answers

Question 1

A developer is processing a large log file and needs to store unique IP addresses to count the visitors. The order of the IP addresses is not important. Which data structure is the most memory-efficient and performant for this specific task?

Accepted Answer

A set, because it only stores unique elements.

Answer

A set is the ideal choice because it enforces uniqueness automatically and provides highly efficient membership testing. While a dictionary could work, it would waste memory storing `None` or a dummy value for each key. Lists and tuples do not enforce uniqueness, requiring extra processing to filter out duplicates.

Question 2

What is a key characteristic of the objects returned by the `.keys()`, `.values()`, and `.items()` methods of a dictionary in Python 3?

Accepted Answer

They are dynamic views that reflect subsequent changes to the dictionary.

Answer

In Python 3, these methods return dictionary view objects. A key feature of view objects is that they are dynamic and provide a live view into the dictionary's entries. If the dictionary is modified, the view object reflects these changes immediately.

Question 3

Which of the following lines of code will result in a `TypeError`?

Accepted Answer

my_dict = {['user', 'id']: 123}

Answer

Dictionary keys must be of an immutable (and hashable) type. Lists are mutable, so they cannot be used as dictionary keys, which will raise a `TypeError`. Tuples, integers, strings, and frozensets are all immutable and can be used as keys or stored in sets.

Question 4

A programmer needs to find elements that are present in `set_A` but NOT in `set_B`. Which set operation should be used?

Accepted Answer

set_A.difference(set_B)

Answer

The `.difference()` method (or the `-` operator) returns a new set containing elements that are in the first set but not in the second set. `union()` combines all elements, `intersection()` finds common elements, and `symmetric_difference()` finds elements that are in either set, but not both.

Question 5

Consider the following code snippet. What will be the final content of `inventory`?

```python
inventory = {'apples': 10, 'oranges': 5}
updates = {'oranges': 15, 'grapes': 20}
inventory.update(updates)
```

Accepted Answer

{'apples': 10, 'oranges': 15, 'grapes': 20}

Answer

The `.update()` method merges the keys and values from one dictionary into another. If a key already exists in the original dictionary, its value is updated with the value from the new dictionary. If a key does not exist, the new key-value pair is added.

Python Practice Test

Python Practice Test

Python Data Structures: Dictionaries and Sets Questions and Answers