Without explanation, Chapter 2 presents the following Python program, but here shown with numbers to the left of each line in the program.

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from turtle import *
from math import *
pensize(10)
pencolor("blue")
penup()
goto(20,0)
pendown()
for i in range(1,101):
  newangle = 2*i*pi/100
  goto( 20*cos(newangle), 
        20*sin(newangle) ) 
Here is a line-by-line explanation of what the program does.

The Point

In a sense, the program shown is a mixture of three languages: Python, mathematics, and a specialized turtle language for drawing. This is typical of all modern software: multiple languages, some specific to the job, are combined to get results. Some of these are not formally developed as languages (they may be libraries of software, so-called development kits, and the like), but the idea of mixing from different sources is fundamental. Programs are mashups.