Teach Your Kids To Code: A Parent-friendly Guide to Python Programming

56 Chapter 4

numbers, you can enter different numbers inside the parentheses

of the range() function:

>>> list(range(3))

[0, 1, 2]

>>> list(range(5))

[0, 1, 2, 3, 4]

As you can see, entering list(range(3)) gives you a list of three

numbers starting at 0, and entering list(range(5)) gives you a list

of five numbers starting at 0.

Using a for Loop to Make a Rosette with Four Circles

For our four-circle rosette shape, we need to repeat drawing a

circle four times, and range(4) will help us do that. The syntax,

or word order, of our for loop will look like this:

for x in range(4):

We start with the keyword for and then we give a variable,

x, that will be our counter or iterator variable. The in keyword

tells the for loop to step x through each of the values in the range

list, and range(4) gives the loop a list of the numbers from 0 to 3,

[0,1,2,3], to step through. Remember that the computer usually

starts counting from 0 instead of starting from 1 as we do.

To tell the computer which instructions are supposed to be

repeated, we use indentation; we indent each command that we

want to repeat in the loop by pressing the tab key in the new

file window. Type this new version of our program and save it as

Rosette4.py.

Rosette4.py

import turtle

t = turtle.Pen()

for x in range(4):

t.circle(100)

t.left(90)

This is a much shorter version of our Rosette.py program,

thanks to the for loop, yet it produces the same four circles as

the version without the loop. This program loops through lines 3,