3.14. A Few More turtle Methods and Observations

Here is a table that summarizes common Turtle methods:

Method	Parameters	Description
Turtle	None	Creates and returns a new turtle object
forward	distance	Moves the turtle forward
backward	distance	Moves the turle backward
right	angle	Turns the turtle clockwise
left	angle	Turns the turtle counter clockwise
up	None	Picks up the turtle’s tail (pen)
down	None	Puts down the turtle’s tail (pen)
color	color name	Changes the color of the turtle and pen
fillcolor	color name	Changes the color the turtle will use to fill a polygon
heading	None	Returns the current heading
position	None	Returns the current position
goto	x,y	Move the turtle to position x,y
begin_fill	None	Remember the starting point for a filled polygon
end_fill	None	Close the polygon and fill with the current fill color
dot	None	Leave a dot at the current position
stamp	None	Leaves an impression of a turtle shape at the current location
shape	shapename	Can be set to ‘arrow’, ‘triangle’, ‘classic’, ‘turtle’, ‘circle’, or ‘square’
speed	integer	0 = no animation, fastest; 1 = slowest; 10 = very fast

Here are a few more things that you might find useful as you write programs that use turtles.

• Turtle methods can use negative angles or distances. So tess.forward(-100) will move tess backwards, and tess.left(-30) turns her to the right. Additionally, because there are 360 degrees in a circle, turning 30 to the left will leave you facing in the same direction as turning 330 to the right! (The on-screen animation will differ, though — you will be able to tell if tess is turning clockwise or counter-clockwise!)

  This suggests that we don’t need both a left and a right turn method — we could be minimalists, and just have one method. There is also a backward method. (If you are very nerdy, you might enjoy saying alex.backward(-100) to move alex forward!)

  Reviewing a few basic facts about geometry and number lines, like we’ve done here, is a good start if we’re going to play with turtles.

• A turtle’s pen can be picked up or put down. This allows us to move a turtle to a different place without drawing a line. The methods are up and down. Note that the methods penup and pendown do the same thing.

  alex.up()
  alex.forward(100)     # this moves alex, but no line is drawn
  alex.down()
  

• Every turtle can have its own shape. The ones available “out of the box” are arrow, blank, circle, classic, square, triangle, turtle.

  ...
  alex.shape("turtle")
  ...
  

• You can speed up or slow down the turtle’s animation speed. (Animation controls how quickly the turtle turns and moves forward). Speed settings can be set between 1 (slowest) to 10 (fastest). But if you set the speed to 0, it has a special meaning — turn off animation and go as fast as possible.

  alex.speed(10)
  

• A turtle can “stamp” its footprint onto the canvas, and this will remain after the turtle has moved somewhere else. Stamping works even when the pen is up.

Let’s do an example that shows off some of these new features. Note that the code below uses a for loop to make the turtle move repeatedly 30 times. We’ll cover for loops in the next chapter.

import turtle wn = turtle.Screen() wn.bgcolor("lightgreen") tess = turtle.Turtle() tess.color("blue") tess.shape("turtle") dist = 5 tess.up() # this is new for _ in range(30): # start with size = 5 and grow by 2 tess.stamp() # leave an impression on the canvas tess.forward(dist) # move tess along tess.right(24) # and turn her dist = dist + 2 tess.color("red") wn.exitonclick()

One more thing to be careful about. All except one of the shapes you see on the screen here are footprints created by stamp. After the loop, we change tess to be red, and that way you see where the actual turtle is (the red one is not a stamp - it’s tess!).

Mixed up program

The following program uses the stamp method to create a circle of turtle shapes as shown to the left:

But the lines are mixed up. The program should do all necessary set-up, create the turtle, set the shape to “turtle”, and pick up the pen. Then the turtle should repeat the following ten times: go forward 50 pixels, leave a copy of the turtle at the current position, reverse for 50 pixels, and then turn right 36 degrees. After the loop, set the window to close when the user clicks in it.

Drag the blocks of statements from the left column to the right column and put them in the right order with the correct indention. Click on Check Me to see if you are right. You will be told if any of the lines are in the wrong order or are incorrectly indented.

        import turtle
wn = turtle.Screen()
jose = turtle.Turtle()
jose.shape("turtle")
jose.penup()
---
for size in range(10):
---
  jose.forward(50)
---
  jose.stamp()
---
  jose.forward(-50)
---
  jose.right(36)
---
wn.exitonclick()
        

Mixed up program

The following program uses the stamp method to create a line of turtle shapes as shown to the left:

But the lines are mixed up. The program should do all necessary set-up, create the turtle, set the shape to “turtle”, and pick up the pen. Then the turtle should repeat the following three times: go forward 50 pixels and leave a copy of the turtle at the current position. After the loop, set the window to close when the user clicks in it.

Drag the blocks of statements from the left column to the right column and put them in the right order with the correct indention. Click on Check Me to see if you are right. You will be told if any of the lines are in the wrong order or are incorrectly indented.

        import turtle
wn = turtle.Screen()
---
nikea = turtle.Turtle()
---
nikea.shape("turtle")
---
nikea.penup()
---
for size in range(3):
---
  nikea.forward(50)
---
  nikea.stamp()
---
wn.exitonclick()
        

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