1) Object-Oriented Programming

Object-Oriented Programming

Python is an object-oriented programming language. That means it provides features that support object-oriented programming (OOP).

Object-oriented programming has its roots in the 1960s, but it wasn’t until the mid 1980s that it became the main programming paradigm used in the creation of new software. It was developed as a way to handle the rapidly increasing size and complexity of software systems and to make it easier to modify these large and complex systems over time.

Up to now, some of the programs we have been writing use a procedural programming paradigm. In procedural programming the focus is on writing functions or procedures which operate on data. In object-oriented programming the focus is on the creation of objects which contain both data and functionality together. Usually, each object definition corresponds to some object or concept in the real world and the functions that operate on that object correspond to the ways real-world objects interact.

A change of perspective

Throughout the earlier chapters, we wrote functions and called them using a syntax such asdrawCircle(tess). This suggests that the function is the active agent. It says something like, “Hey, drawCircle! Here’s a turtle object for you to use to draw with.”

In object-oriented programming, the objects are considered the active agents. For example, in our early introduction to turtles, we used an object-oriented style. We said tess.forward(100), which asks the turtle to move itself forward by the given number of steps. An invocation like tess.circle() says “Hey tess! Please use your circle method!”

This change in perspective is sometimes considered to be a more “polite” way to write programming instructions. However, it may not initially be obvious that it is useful. It turns out that often times shifting responsibility from the functions onto the objects makes it possible to write more versatile functions and makes it easier to maintain and reuse code.

The most important advantage of the object-oriented style is that it fits our mental chunking and real-life experience more accurately. In real life our cook method is part of our microwave oven — we don’t have a cook function sitting in the corner of the kitchen, into which we pass the microwave! Similarly, we use the cellphone’s own methods to send an sms, or to change its state to silent. The functionality of real-world objects tends to be tightly bound up inside the objects themselves. OOP allows us to accurately mirror this when we organize our programs.

Objects Revisited

In Python, every value is actually an object. Whether it be a turtle, a list, or even an integer, they are all objects. Programs manipulate those objects either by performing computation with them or by asking them to perform methods. To be more specific, we say that an object has a state and a collection of methods that it can perform. The state of an object represents those things that the object knows about itself. For example, as we have seen with turtle objects, each turtle has a state consisting of the turtle’s position, its color, its heading and so on. Each turtle also has the ability to go forward, backward, or turn right or left. Individual turtles are different in that even though they are all turtles, they differ in the specific values of the individual state attributes (maybe they are in a different location or have a different heading).