5.6. A Few More
turtle Methods and Observations¶
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
down. Note that the methods
pendowndo 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
... 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.
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.
If you are curious about how far the turtle is traveling each time the for loop iterates, you can add a print
statement inside of the for loop to print out the value of
One more thing to be careful about. All except one of the shapes you see on the screen here are
footprints created by
stamp. But the program still only has one turtle instance — can you
figure out which one is the real tess? (Hint: if you’re not sure, write a new line of code after the
for loop to change tess’ color, or to put her pen down and draw a line, or to change her shape, etc.)
Mixed up program
Mixed up program