DICTIONARIES

Python has a key/value structure called a dictionary (dict) that is a hash table. A dictionary (and hash tables in general) can retrieve the value of a key in constant time, regardless of the number of entries in the dictionary (and the same is true for sets). You can think of a set as essentially just the keys (not the values) of a dict implementation.

The contents of dict can be written as a series of key:value pairs, as shown here:

dict1 = {key1:value1, key2:value2, ... }

The “empty dict” is just an empty pair of curly braces {}.

Creating a Dictionary

A dictionary (or hash table) contains of colon-separated key/value bindings inside a pair of curly braces:

dict1 = {}

dict1 = {'x' : 1, 'y' : 2}

The preceding code snippet defines dict1 as an empty dictionary, and then adds two key/value bindings.

Displaying the Contents of a Dictionary

You can display the contents of dict1 with the following code:

>>> dict1 = {'x':1...