Adding and updating key-value pairs in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

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

You add a new key-value pair by assigning a value to a new key using square brackets. For example: my_dict['new_key'] = 'new_value'.

beginner

What happens if you assign a value to an existing key in a Python dictionary?

The existing key's value is updated (replaced) with the new value. For example, my_dict['key'] = 'new_value' changes the old value to 'new_value'.

intermediate

Show how to add multiple key-value pairs to a dictionary at once.

Use the update() method with another dictionary or iterable of pairs. Example: my_dict.update({'a': 1, 'b': 2}) adds or updates keys 'a' and 'b'.

intermediate

Can you use the setdefault() method to add a key-value pair? How?

Yes. setdefault(key, default_value) adds the key with default_value if the key is not present. If the key exists, it returns its value without changing it.

intermediate

What is the difference between adding a key-value pair using assignment and using update()?

Assignment adds or updates a single key-value pair: my_dict[key] = value. update() can add or update multiple pairs at once from another dictionary or iterable.

What does this code do?
my_dict['color'] = 'blue'

A Adds or updates the key 'color' with value 'blue'

B Deletes the key 'color'

C Checks if 'color' is in the dictionary

D Creates a new dictionary

Assigning a value to a key adds it if missing or updates it if present.

Which method adds multiple key-value pairs to a dictionary at once?

A append()

B update()

C insert()

D add()

update() merges another dictionary or iterable of pairs into the dictionary.

What does setdefault('key', 0) do if 'key' is already in the dictionary?

A Updates 'key' to 0

B Removes 'key'

C Returns the current value of 'key' without changing it

D Raises an error

setdefault returns the existing value if the key exists.

If you want to change the value of an existing key, what should you do?

A Assign a new value to the key using <code>[]</code>

B Use <code>del</code> then add new key

C Use <code>pop()</code>

D Use <code>clear()</code>

Assigning a new value to the key updates it directly.

What will this code do?
my_dict.update({'x': 10, 'y': 20})

A Create a new dictionary with keys 'x' and 'y'

B Delete keys 'x' and 'y'

C Raise an error

D Add or update keys 'x' and 'y' with values 10 and 20

update() adds or updates multiple key-value pairs.

Explain how to add a new key-value pair and update an existing key in a Python dictionary.

Think about using square brackets with the key.

Describe the difference between using assignment and the update() method to add or update dictionary entries.

One is for one pair, the other can handle many.