Abstract Differences Between Lists and Dictionaries

Dictionaries are similar to lists, except instead of using a numerical index to insert and retrieve an "item", you use a key and value. For example, if you think of a dictionary as a phone book, the key would be a person's name, and the value would be their phone number. How do you find someone's phone number? You use their name to look it up!

Every key in a dictionary must be unique so that we know which value to return for a given key. But dictionaries are NOT sorted. What makes dictionaries useful is that we assign a key to each value, instead of a numerical index like we do for a list. Here are visual examples of a list and a dictionary to help you understand the difference: