Python – Data Structures: Dictionaries

Dictionaries

Dictionaries are slightly different than the rest. In dictionaries we supply our own indexes. The index is often referred to as a key. Keys can be strings, integers, floats, or even tuples.  We then supply the value of the key.

You might have noticed that dictionaries require a different structure within the brackets to assign keys to the values. They use a colon : to separate the value from its key.

Example of a dictionary

my_dictionary = {1:"cat", 2:"dog", 3:"horse", 4:"fish"}

or

my_dictionary2 = {"1":"cat", "2":"dog", "3":"horse", "4":"fish"}

We can look up items by referring to their keys

my_dictionary[2] 
-> "dog"

my_dictionary["3"]  
-> "horse"

We can add new items to a dictionary by placing the item in square brackets like this:

my_dictionary[5] = "monkey"
print(my_dictionary)
-> {1: 'cat', 2: 'dog', 3: 'horse', 4: 'fish', 5: 'monkey'}

We can check whether a value is in a dictionary the same way we check whether a value is in a list or set with the in keyword. Dictionaries also have a method that’s also useful, get. get looks up values in a dictionary, but unlike square brackets, get returns None (or a default value of your choice) if the key isn’t found.

print("dog" in my_dictionary)
-> True

print(my_dictionary.get("gopher"))
-> False

Identity Operators

Compound Data Structures

We can have dictionaries inside dictionaries so that we are able to store more information.

Sort of like our contacts app

contacts = {"Sally":{"number": 1234567890, "email":"sally@gmail.com", "dob":"01-01-1980"}, "Bob"{"number": 2345678901, "email":"bob@gmail.com", "dob":"02-01-1998"}}

We now have two contacts and we can access Sally’s email by doing

sally_email = contacts["Sally"]["email"]

We can also add a new contact

Martha = {"number":5678901234, "email":"martha@gmail.com", "dob":"11-11-2000"}
contacts["Martha] = Martha

This is from Lesson 22:  Data Types and Operators Videos 29-35