1.4. Compute with Turtles¶
The idea of “turtle programming” dates back to the 1960’s and originated with Seymour Papert. He developed a robot turtle with a physical pen in it. Children would steer the robot around and create drawings with the pen by writing programs in a language called Logo.
Today, we can play with virtual turtles in a fully-graphical and non-robotic way. To do so, we
will make use of another feature of Python - code libraries. A library is a collection of
existing code designed to help programs perform some task. Using a library means we do not have
to figure out how to handle all the details of a particular problem - the library code will
take care of many of those details for us. In the case of making a virtual turtle, our program
will need to have a way to keep track of where the turtle is, a way to move the turtle around,
a way to draw to the screen, etc… The
turtle library will handle these details for us.
To use a library, we need to tell Python we want to use the library with an import statement.
In the program below, we start with
import turtle to tell Python we want to make use
of the turtle library. To use commands from the library, we use dot notation: we type the
name of the library, then a dot ., then the command.
alex = turtle.Turtle() calls the Turtle() command from the turtle library to
make a new turtle - we name that turtle alex.
The turtles that we make are objects that have behaviors we can access
with dot-notation. We use these to tell the turtle
alex to move around on the screen using
alex.forward(150). As the turtle moves around it draws a line behind itself.
Just by going forward, backward, left, and right, we can have a turtle draw a shape: