Dictionaries and key-value pairs in Intro to Computing - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a dictionary in computing?

A dictionary is a collection that stores data in pairs called key-value pairs. Each key is unique and is used to find its matching value, like looking up a word in a real dictionary to find its meaning.

beginner

Explain the term 'key' in a dictionary.

A key is a unique identifier used to access a value in a dictionary. Think of it like a label on a box that tells you what's inside.

beginner

How does a dictionary differ from a list?

A dictionary uses keys to find values, while a list uses numbered positions (indexes). It's like a phone book (dictionary) versus a numbered seating chart (list).

intermediate

What happens if you try to use a key that does not exist in a dictionary?

You get an error or a special response saying the key is not found, similar to looking up a word that isn't in a dictionary.

intermediate

Can keys in a dictionary be changed after creation?

No, keys are fixed and must be unique. However, the values they point to can be changed. It's like a label on a jar—you can't change the label, but you can change what's inside the jar.

What does a dictionary store?

A Pairs of keys and values

B Only values

C Only keys

D Ordered list of items

A dictionary stores data as pairs of keys and values, where each key is unique.

Which of these is a valid key in a dictionary?

A An index number

B A unique label

C A repeated value

D A number only

Keys must be unique labels to identify values in a dictionary.

If you want to find a value in a dictionary, you use the:

A Value

B Index

C Key

D Position

You use the key to look up the matching value in a dictionary.

What happens if you try to access a key that does not exist?

A You get an error or 'not found' message

B You get the first value

C You get a random value

D The dictionary adds the key automatically

Accessing a non-existent key usually causes an error or a 'not found' response.

Can dictionary keys be changed after they are created?

A Keys can be changed only if values are numbers

B Yes, keys can be changed anytime

C Keys change automatically

D No, keys cannot be changed

Keys are fixed and cannot be changed once set; only values can be updated.

Describe what a dictionary is and how it stores data.

Think about how a phone book or a real dictionary works.

Explain the difference between a dictionary and a list.

Compare a phone book to a numbered seating chart.