Practical Programming, 2nd Edition

Writing a Method in Class Book

As you saw in Chapter 7, ​Using Methods​, there are two ways to call a method. One way is to access the method through the class, and the other is to use object-oriented syntax. These two calls are equivalent:

>>> str.capitalize('browning')
'Browning'
>>> 'browning'.capitalize()
'Browning'

We’d like to be able to write similar code involving class Book. For example, we might want to be able to ask how many authors a Book has:

>>> Book.num_authors(ruby_book)
3
>>> ruby_book.num_authors()
3

To get this to work, we’ll define a method called num_authors inside Book. Here it is:

class Book:
    """Information about a book."""

    def num_authors(self):
        """ (Book) -> ...