Exploring an Interface Example

00:00 In this video, you’ll be looking at a real-life example. You’ll be looking at the dir() function. We’ll be using that function to investigate the string class or the str class from the built-in functions in the Python standard library.

00:14 So please move to your REPL. So in your terminal, you start your REPL, as we have done before using python or python 3. You see the three arrows in front of your cursor so you are in the REPL, and you type in dir(

00:31 str), press Enter. And now you can see all the objects that are available in the string class, the str class. So you have __add__, __class__, lots of those that have underscores.

00:47 One of those is __init__. But then there’s also quite a few that don’t start with an underscore: capitalize(), casefold(), center(), count(), and so on.

01:01 So what have you learned from the dir() example or the str example? There were some public methods there: isnumeric(), replace(), split(), so they don’t start with an underscore.

01:13 There were special methods there: __add__, __init__. That’s quite a tongue twister. So that’s double underscore add, double underscore, or a dunder method.

01:25 And we will talk about those in more detail later in the course. But there were a few of those with two leading and two trailing underscores. Were there any non-public ones starting with a single underscore?

01:38 I didn’t see one, but let’s have a look at the output.

01:43 I don’t see any that starts with an underscore. I see format_map(), which clearly has an underscore, but it doesn’t start with one.

01:54 So none of the non-public methods starting with a single underscore. And I also didn’t see any starting with a double underscore that did not end with two underscores.

02:05 So no non-public methods starting with a double underscore.

02:10 So now that you know the difference between a public and a non-public interface, you are ready to tackle single leading underscores. See you in the next lesson.