Dictionaries

The first data structure we're going to look at is Python's dictionary. A dictionary consists of any number of key-value pairs. The key can be used to get or set the value or remove the pair from the dictionary entirely.

There are several ways to create a dictionary in Python. The simplest is to use a dictionary expression, which is just a pair of curly brackets surrounding the key-value pairs we want in the dictionary. Each key-value pair is marked with a colon between the key and value, and each pair is separated by a comma, as shown in the following code example:

example_dict = {'a' :1, 'b' :2, 'c' :3} 

When this expression runs, the result is a dictionary object containing the keys and their values. We can also use the dict class to create dictionary objects:

another_dict = dict() 

If we don't want to use the special syntax to access one of the stored values in a dictionary, we use a lookup expression. This means that we place square brackets containing the key we want to look up after an expression that gives us the dictionary. Usually, this means, the name of the variable containing the dictionary, an open square bracket, a sub-expression that gives us the key, and then a closing square bracket:

example_dict['b'] 
2 

We can also use the dict.get function if we prefer not to use the special syntax:

example_dict.get('c') 
3