Diving Deeper Into Magic Methods

00:00 You might be wondering, I’ve seen len two different ways, sometimes with double underscores and sometimes without any underscores, like a function.

00:09 What’s the difference? The double-underscore version is the special method implemented in classes, and the non-underscore version is the built-in function that calls this special method.

00:23 The difference is in how these methods are typically used. When you use the .__len__ magic method directly, you are calling the magic method yourself.

00:34 However, when you use the built-in function, len(), Python is implicitly calling the len dunder method for you. This pattern of using a built-in function that internally calls a magic method applies to many operations in Python.

00:52 You’ll learn about them in the next lessons so let’s just stick with the len example for now.

00:59 In this example, you have a BookCollection class that takes a list of books as an argument. The __init__() method initializes the object with the list of books storing it in the .self.books attribute.

01:14 Next, you’re defining the len magic method, which is for determining the length of the book collection. This method returns the length of the .self.books list using Python’s built-in len function.

01:29 Now, when you create a BookCollection instance with books, Book 1, Book 2, and Book 3, and then call len(collection), what happens behind the scenes is that Python implicitly calls the len magic method of the collection object.

01:46 This method calculates the length of .self.books, which in this case is three, and returns that value. So print(len(collection)) outputs three.

01:59 Why would I use the len function and not just directly use the magic method? Well, the len function is a more intuitive and user-friendly way.

02:08 You could directly call the magic method, but using the len built-in function is considered more Pythonic because it’s more straightforward and more readable.

02:19 Python automatically calls the dunder method when you call len, making your code cleaner and more understandable.