Creating dictionaries#

Every element in a dictionary is a key-value pair and a dictionary contains a collection of these key-value pairs. A key-value pair is some key with its associated value. To create a dictionary, we use curly braces {} and provide some key-value pair(s) separated by commas. Each key-value pair is created in a dictionary using this syntax key:value.

Below we have created a dictionary and assigned it to the variable class_dict. This dictionary contains the number of people in this class by their role.

class_dict = {'instructors': 1, 'CAs': 2, 'students': 59}

Each key is a string that denotes the role. We have 3 keys in class_dict which represent 3 different roles: 'instructors', 'CAs', and 'students'. Each value is an integer that represents the number of people with that particular role. The corresponding values in this dictionary are 1, 2, and 59. After associating the values to the keys, we have 3 key-value pairs: 'instructors': 1, 'CAs': 2, and 'students': 59. Notice that these key-value pairs are within the curly braces and separated by commas. In this class_dict dictionary, we have 1 instructor, 2 CAs, and 59 students.

Below we have created another dictionary using integers for the key and strings for the value. This employees dictionary contains employee IDs and the corresponding employee name. Each key is an employee ID and each value is a name. Notice that compared to lists which have indexes that start at 0, dictionary keys can be any integer.

employees = {2201: 'Joseph Warmus', 548 : 'Annie Wai'}

In this employees dictionary, we have 2 employees. The employee ID, 2201, corresponds to 'Joseph Warmus', and 548 corresponds to 'Annie Wai'.

The dict type#

Dictionaries in Python are of type dict. You can use the type dict in a few ways: to create or copy a dictionary and in tests with isinstance.

A dictionary is like a list of tuples, but it’s much faster to work with keys in dictionaries than it is in lists. Let’s learn more!