Think Python, 3rd Edition

Chapter 15. Classes and Methods

Python is an object-oriented language—that is, it provides features that support object-oriented programming, which has these defining characteristics:

• Most of the computation is expressed in terms of operations on objects.

• Objects often represent things in the real world, and methods often correspond to the ways things in the real world interact.

• Programs include class and method definitions.

For example, in the previous chapter we defined a Time class that corresponds to the way people record the time of day, and we defined functions that correspond to the kinds of things people do with times. But there was no explicit connection between the definition of the Time class and the function definitions that follow. We can make the connection explicit by rewriting a function as a method, which is defined inside a class definition.

Defining Methods

In the previous chapter, we defined a class named Time and wrote a function named print_time that displays a time of day:

class Time:
    """Represents the time of day."""

def print_time(time):
    s = f'{time.hour:02d}:{time.minute:02d}:{time.second:02d}'
    print(s)
       

To make print_time a method, all we have to do is move the function definition inside the class definition. Notice the change in indentation.

At the same time, we’ll change the name of the parameter from time to self. This change is not necessary, but it is conventional for the first parameter of a method to be named self:

class Time:
    """Represents ...