Accessing values using keys in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a key in a Python dictionary?

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

beginner

How do you access a value using a key in a Python dictionary?

You use square brackets with the key inside, like dictionary[key]. This tells Python to find the value linked to that key.

beginner

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

Python will give a KeyError. It's like asking for a box that isn't there.

intermediate

How can you safely access a value for a key that might not exist?

Use the get() method, like dictionary.get(key, default). It returns the value if the key exists, or a default value if it doesn't.

beginner

Example: Given person = {'name': 'Alice', 'age': 30}, how do you get Alice's age?

Use person['age']. This will give you 30, the value linked to the key 'age'.

What will my_dict['color'] return if my_dict = {'color': 'blue'}?

A None

B 'blue'

C KeyError

D 'color'

Accessing the key 'color' returns its value 'blue'.

What error occurs if you access a missing key in a dictionary using square brackets?

A TypeError

B ValueError

C KeyError

D IndexError

Trying to access a key that doesn't exist raises a KeyError.

Which method allows safe access to a dictionary key with a default value?

A dictionary.get()

B dictionary.find()

C dictionary.access()

D dictionary.lookup()

The get() method returns the value or a default if the key is missing.

If data = {'x': 10}, what does data.get('y', 0) return?

A KeyError

B None

C 10

D 0

Since 'y' is missing, get() returns the default value 0.

How do you access the value for key 'name' in info = {'name': 'Bob'}?

A info['name']

B info.get_name()

C info.name

D info.get('age')

Use square brackets with the key string: info['name'].

Explain how to access a value in a Python dictionary using a key.

Think about how you find a labeled box in a shelf.

Describe how to safely get a value from a dictionary when the key might not exist.

It's like asking politely and getting a backup answer.