Defining Classes with Data from the Internet¶

Considering those questions when you write a new class definition is always important, but it can be especially tricky when you are using classes to deal with data that you get from an API request.

Using the iTunes Search API as an example, we’ll look at an example of defining a class to represent a song.

This API has several parameters, some of which are optional. The ones we’ll care about for now are term, whose value is a string term to search for (the beatles maybe), and entity, which can be song or album.

You can read the documentation and make a few requests to the API to see what the nested data response you get looks like.

It turns out that if you make a request like this:

resp = requests.get("https://itunes.apple.com/search",params={"term":"beatles","entity":"song"}).json()

you get data back that includes a big list of dicitionaries that represent songs. You have to parse through the nested data a little bit to save that list in a variable (remember the Nested Data Structures chapter), but once you’re there, you can play around with it and look at the information it contains.

It’s a little difficult to parse (try using the API yourself, and look back at the Nested Data chapter!), but for the purposes of this chapter, we can skip ahead to the class definition.

You know that once you’ve made a request to this API and gotten some data, you’ll be able to access a bunch of dictionaries, and each dictionary holds a bunch of information about a song.

Next, you can answer the questions we posed in the last section about your class definition. Here, we’ll choose some answers so we can write an example class definition – but the way you answer these questions will depend upon what program you want to write! If you want your class instances to be able to do slightly different things, you would write different methods. If different information is important to you, you would create different instance variables, and so on.

What is the data that you want to deal with? Dictionaries that represent songs, where each contains key-value pairs that hold information about a song.

What will one instance of your class represent? One song.

What information should each instance have as instance variables? Each instance represents one song, and each song has an artist and a title as instance variables.

What instance methods should each instance have? Each song instance should have a method that returns the artist’s name. And each song instance should have a method that returns the number of vowels in the song’s title. (Maybe because you want to do some linguistic analysis about song titles in your program.)

What should the printed version of an instance look like? A printed version of a song instance should show the song title and the artist’s name.

Finally, you should ask yourself: what information gets passed into the constructor of the class to create an instance of this class?

In this case, you have a bunch of dictionaries available in the data you got back from the API request above. And each dictionary represents a song. So you can pass in a song dictionary to the constructor!

Below is an example of the class definition we just described. (You can’t run this code and create instances here with live data because we can’t use the requests module in the textbook environment, but you can copy this into a program file of your own and play with it!)