4. Turtle Racing¶

Walkthrough¶

Zach and Jesse have had a long day working at LaunchCode, so after work they go to Dressel’s Pub down the street to blow off some steam. Problem is, they blow off a bit too much steam. Upon leaving, they have completely lost their sense of direction and each walks in random directions.

We will write a program with Turtles to simulate their journey after leaving the pub.

import turtle import random win = turtle.Screen() # create 2 turtles zach = turtle.Turtle() jesse = turtle.Turtle() # speed them up! zach.speed(10) jesse.speed(10) jesse.color("green") zach.color("orange") # make them walk randomly, loop variable represents distance to travel forward for distance in range(0,50,2): # generates [0,2,4,6,8,10,12,...46,48] # create a random angle for each turtle zach_angle = random.randrange(0,181) jesse_angle = random.randrange(0,181) # turn each turtle in that random direction zach.left(zach_angle) jesse.left(jesse_angle) # move each turtle forward by distance zach.forward(distance) jesse.forward(distance)

Studio¶

In this studio we are going to work step by step through the problem of racing turtles. The idea is that we want to create two or more turtles and have them race across the screen from left to right. The turtle that goes the farthest is the winner.

There are several different, and equally plausible, solutions to this problem. Let’s look at what needs to be done, and then look at some of the options for the solution. When you are faced with a problem like this in computer science it is often a good idea to find a solution to a simple problem first and then figure out how to make the solution more general. So to start, let’s think about a solution to the simplest form of the problem, a race between two turtles. We’ll look at more complex races later.

Here is a possible sequence of steps that we will need to accomplish:

1. Import the modules we need
2. Create a screen
3. Create two turtles
4. Move the turtles to their starting positions
5. Send them racing across the screen

Here is the Python code for the first 4 steps above. Continue below for a discussion on possible solutions.

import turtle # 1. import the modules import random wn = turtle.Screen() # 2. Create a screen wn.bgcolor('lightblue') lance = turtle.Turtle() # 3. Create two turtles andy = turtle.Turtle() lance.color('red') andy.color('blue') lance.shape('turtle') andy.shape('turtle') andy.up() # 4. Move the turtles to their starting point lance.up() andy.goto(-100,20) lance.goto(-100,-20) # your code goes here wn.exitonclick()

You have several choices for how to fill in the code for step 5. Below are some possibilities. Try coding each of the following in the box above to see the different kinds of behavior.

1. Use a single call to forward for each turtle, using a random number as the distance to move.
2. Create a for loop, using a random number for the argument passed to the range function. Inside the for loop move each of the turtles forward by some random number of units.
3. Be creative! What other ways might you simulate a race between two participants?

So, which of these programs is better? Which of these programs is most correct? These are excellent questions. Program 1 is certainly the simplest, but it isn’t very satisfying as far as a race is concerned. Each turtle simply moves their distance on their turn. Program 2 is probably the most “realistic” assuming realism is very important when we’re talking about a simulated race of virtual turtles.

You may be thinking why can’t each turtle just move forward until they cross some artificial finish line? Good question! We’ll get to the answer to this, and look at the program in a later lesson, when we learn about something called the while loop.