Lesson #8: Dictionaries

As you’ve already seen, dictionaries are a data type similar to arrays but work with keys and values instead of indexes. It is generally used when we have a huge amount of data. Also, dictionaries are optimized for retrieving data.

Reminder: Dictionaries are written with curly brackets, and have keys and values.

Example

Accessing Dictionary Values

To access a value in a dictionary, enclose the corresponding key in square brackets ([]) at the end of the dictionary or a variable name assigned to a dictionary.

Adding and Removing Values

Dictionaries are mutable data structures which means you can add and remove items.

Add Value

Let’s add the name of a customer to the customers dictionary:

Remove Value

To remove an item from a dictionary, use the del keyword with the key for the value you want to delete.

Let’s remove the name of a customer from the customers dictionary:

Loop Through Dictionaries

When you loop over a dictionary with a for loop, you iterate over the dictionary’s keys:

The following example loop over a dictionary and prints all the values.

Example

Nested Dictionaries

A dictionary can contain dictionaries, this is called nested dictionaries. Let’s alter the customers dictionary to illustrate the following idea:

Instead of mapping customers’ names to their details, you created a dictionary that maps each customer’s name to a dictionary containing the name and the age. The value of each key is a dictionary: