Learning Python with Raspberry Pi

Chapter 2

A Really Quick Introduction to Python

IN THIS CHAPTER, you'll dive right into some code examples. Don't expect to grasp all the details yet. This chapter is meant to give you a taste of programming. You'll learn how to draw on the screen, and even how to make a simple game. Along the way you'll pick up some basic programming concepts, but don't worry if you don't understand every line of every program you create in this chapter. You'll learn more about the details in later chapters.

Drawing Picture with Turtles

It's time to get programming! We strongly recommend that you enter the code into IDLE 3 as you read along, as it will help you understand what's happening. So, without further ado, open IDLE 3, go to File⇒New Window, and enter the following:

import turtlewindow = turtle.Screen()babbage = turtle.Turtle()babbage.left(90)babbage.forward(100)babbage.right(90)babbage.circle(10)window.exitonclick()

Then go to Run⇒Run Module or press F5 to execute the program. A dialog will open and ask you to provide a filename. This name can be whatever you want, although it helps if it's descriptive so you'll remember it in the future (we used chapter2-example1.py).

Each of these lines is an instruction to Python. Python goes through them one-by-one and executes them in the order it finds them. The result of the computer following all these steps is to draw a line with a circle on top, as shown in Figure 2-1. You might think the drawing looks like a lollipop, but actually, it's the ...