Dictionary use cases in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a dictionary in Python?

A dictionary is a collection of key-value pairs where each key is unique. It allows fast lookup, insertion, and deletion of values based on keys.

beginner

How can dictionaries be used to count occurrences of items?

You can use a dictionary to store items as keys and their counts as values. Each time an item appears, increase its count in the dictionary.

beginner

Why are dictionaries useful for representing real-world data like a phone book?

Dictionaries map unique keys (like names) to values (like phone numbers), making it easy to find a phone number by name quickly.

intermediate

How can dictionaries help in grouping data?

Dictionaries can group data by using keys as group names and values as lists of items belonging to each group.

intermediate

What is a common use of dictionaries in caching?

Dictionaries store results of expensive computations with input parameters as keys, so repeated calls can return cached results quickly.

Which data structure is best for fast lookup by a unique key?

A List

B Dictionary

C Tuple

D Set

Dictionaries provide fast lookup by unique keys, unlike lists or tuples which require searching.

How do you add a new key-value pair to a dictionary?

A dict.insert(key, value)

B dict.add(key, value)

C dict.append(key, value)

D dict[key] = value

You add or update a key-value pair by assigning value to dict[key].

What happens if you use a key that already exists in a dictionary when assigning a value?

A The key is duplicated

B An error is raised

C The old value is replaced with the new value

D The dictionary ignores the new value

Assigning a value to an existing key updates the value, replacing the old one.

Which of these is NOT a typical use case for dictionaries?

A Storing ordered sequences

B Caching results

C Mapping keys to values

D Counting items

Dictionaries do not store ordered sequences; lists or tuples are better for that.

How can dictionaries help group items by category?

A Use categories as keys and lists of items as values

B Use items as keys and categories as values

C Use lists inside keys

D Dictionaries cannot group items

Grouping is done by using category names as keys and storing lists of items as values.

Explain three common use cases for dictionaries in Python.

Think about how dictionaries store data and how that helps in real-life tasks.

Describe how you would use a dictionary to count how many times each word appears in a list.

Imagine tallying votes or scores using a dictionary.