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14.4. Using Random Numbers

We can generate random numbers in Python using the randrange function in the random library. This function takes an optional starting value (inclusive) and the ending value for the range (exclusive). We can use random numbers in games to add an element of chance. We can also use random numbers to move the turtle to random positions as shown below. We are using conditionals to alternate the drawing color each time the turtle moves.

from turtle import * # use the turtle library import random space = Screen() # create a turtle screen (space) width = space.window_width() height = space.window_height() maxX = width / 2 # get the max x value minX = -1 * maxX maxY = height / 2 minY = -1 * maxY jaz = Turtle() # create a turtle named jaz for num in range(10): if num % 2 == 0: # if even row jaz.color('red') # set the color to red if num % 2 == 1: # if odd row jaz.color('black') # set the color to black randX = random.randrange(minX, maxX) randY = random.randrange(minY, maxY) jaz.goto(randX,randY)

Can you modify the code above to use 3 different colors? You can use num % 3 to give you 3 possible results.

What could you use to limit the x values to just the left half of the drawing space (screen)?

• randX = random.randrange(minX, maxX)
• This will range from the minimum x value (inclusive) to the maximum x value (exclusive). It will cover the whole width of the drawing area.
• randX = random.randrange(0, maxX)
• This will range from 0 to the maximum x value (exclusive). It will cover the right half of the drawing area.
• randX = random.randrange(minX, 0)
• This will range from the minimum x value (inclusive) to 0. It will cover the left half o the drawing area.

In the first section this chapter we created the chevron image on the left using turtles. Modify the code to create the stampped image on the right. The turtles will stamp/draw in blue and green. The color will be chosen at random.

from turtle import * from sys import * setExecutionLimit(50000) space = Screen() width = 400 space.setup(width,width) maxX = width / 2 jaz = Turtle() jaz.shape('turtle') jaz.penup() jaz.goto(-1 * maxX,100) jaz.pendown() jaz.left(60) for x in range(10): jaz.forward(100) jaz.right(120) jaz.forward(100) jaz.left(120) if (jaz.xcor() >= maxX): jaz.penup() jaz.goto(-1 * maxX,jaz.ycor() - 100) jaz.pendown()

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# CREATE THE TURTLE WORLD from turtle import * import random from sys import * setExecutionLimit(50000) space = Screen() # SET UP THE SCREEN SIZE width = 400 space.setup(width,width) maxX = width / 2 # MOVE TURTLE TO STARTING POSITION jaz = Turtle() jaz.shape('turtle') jaz.penup() jaz.goto(-1 * maxX,100) jaz.pendown() jaz.left(60) # DRAW THE CHEVRON DESIGN for x in range(10): rand = random.randrange(0, 2) if (rand == 0): jaz.color("green") else: jaz.color("blue") jaz.forward(100) jaz.right(120) jaz.stamp() jaz.forward(100) jaz.left(120) if (jaz.xcor() >= maxX): jaz.penup() jaz.goto(-1 * maxX,jaz.ycor() - 100) jaz.pendown()

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