17.9. Project: Local Turtle Races

Hopefully, by the end of this project you will have a program that you just can’t resist running over and over again.

On your mark, get set, go!

You are going to make turtles race across a straight track that is 400 pixels long. The first one to the finish line wins!

17.9.1. Part A: Drawing Space Setup

Open Visual Studio Code and create a new project directory and a turtle_race.py file.

1. In turtle_race.py, import the turtle and random modules.

2. Define a main() function and create a new Screen() object.

3. Use the .title() and .setup() methods on the object to give the drawing window a title and a size of 600 x 600 pixels.

4. The last statement in main() should call the .exitonclick() method on the object.

Run your program to test your window features.

17.9.2. Part B: Create Turtles

Define a function called create_racing_turtle() that:

1. Takes two parameters, one for color and one for shape. Assign the default values 'black' and 'turtle' for these variables.

2. Creates a new turtle object and assigns it the color and shape values.

3. Assigns every turtle the same pensize and speed (3 and 8 are good choices).

4. Returns the new turtle object.

In main(), call the create_racing_turtle function and assign the returned object to a variable. Verify that the function works by drawing a single line with variable_name.forward(100).

Once the function works, use it to create at least 4 turtle objects. Put each of these into a list called racers.

17.9.3. Part C: Start & Finish Lines

Now that you’ve created some racing turtles, you need to draw the finish line and put the objects in their starting positions.

17.9.3.1. Draw the Finish Line

To mark the finish line, you will use an invisible turtle to draw it.

Note

Some of the methods on this page may be unfamiliar to you. That’s OK. We provide directions for how to use each one, and you can always check the Python documentation for more details.

Define a function called draw_finish() that:

1. Takes the length of the racers list as the parameter.

2. Creates a new Turtle object and assigns it to a variable.

3. Calls the .hideturtle() method on the object. Lines will still show up in the drawing space, but the turtle shape will remain invisible. The method requires no arguments inside the parentheses ().

4. Sets the pensize, the speed, and color for the turtle. Feel free to choose any values for these properties you want.

5. Uses the penup, pendown and movement methods to move the turtle forward 200 pixels and then draw a vertical line up towards the top of the screen. The length of the line should depend on how many turtles are in the racers list.

   Finish Line Length

   Number of Turtle Racers	Length in Pixels
   2	50
   3	100
   4	150
   5	200

6. draw_finish does not return any value.

In main(), call draw_finish several times, using different integers for the argument.

17.9.3.2. Place Turtles at Start

With four racing turtles, you need to make a starting lineup that looks something like the figure below. Turtle shapes and colors may vary. The numbers show the object positions compared to the center of the screen.

Turtles start 200 pixels to the right of the center of the screen. The finish line is 200 pixels to the left.

By default, all new Turtle objects start in the center of the drawing space, which has the coordinates (0, 0). This means each new turtle gets stacked on top of all the others. We need to spread them out before they can race!

Define a function called start_positions() that:

1. Takes the racers list as a parameter.

2. Includes a loop to iterate through the list. For each turtle object, use the .goto(x_value, y_value) method to move the turtle to its starting point. goto() places the turtle at a specific spot on the screen. x_value represents the left-right position, and each turtle will use -200 for this.

   y_value represents the up-down position. The first turtle in the list will have a y_value of 0. The second will be 50. The third 100, etc.

   Tip

   Use variables to calculate y_value instead of typing in specific numbers! Hint: Maybe you can relate y_value to an index in the racers list…

3. Returns no value.

In main(), call start_positions several times, placing two or more turtles in the racers list. No matter how many objects are in racers, the start and finish lines should always match in length.

17.9.4. Part D: Run the Race

The statements to control the turtle race go inside the main() function. After setting up the drawing window, your code should:

1. Create the turtles and put the objects in the racers list.

2. Call the draw_finish and start_position functions.

3. Use nested loops to move the turtles:

   1. Every turn, each turtle moves forward a random distance. Values in the range of 5 - 20 pixels are a good place to start, but you can adjust the end points as you wish.

   2. Include a conditional to check each turtle after it moves. The objects all start at -200 and move toward 200. How can you determine if the turtle crossed the finish line? (There are multiple correct ways to do this).

   3. When a turtle crosses the finish line, use the .write() method to display a victory message on the screen!

      turtle_name.write("I win!\t", align='right')
      

4. Ties are possible! When a turtle crosses the finish line, the racing loops should stop. However, they should end AFTER all of the turtles in the list get a chance to move. This means multiple turtles can cross the finish line on the same turn.

   Without this condition, the turtle at index 0 gets a big advantage in the race, since it moves first.

Turtles that reach or move past the finish line in the same turn tie.

Run your program several times to make sure that the same turtle doesn’t always win the race! The results are supposed to be random.

17.9.5. Part E: Bonus Missions

Once you get your four turtles racing, try adding one of these enhanced features:

1. Assign a random color or shape to each turtle.

2. Randomly select the number of turtles to race. Use a loop to create the objects and append them into racers.

3. Add a Replay option to your code to ask the user if they want to run another race.

Enhanced Turtle Racing