My class extension turtlehack

The first thing I did was replace the draw_square method with the draw_polygon method:

 # A method for drawing an arbitrarily many-sided polygon
  def draw_polygon(self, sides, length, x=None, y=None):
    # Draws polygon in place unless a new location is specified
    self.goto(x if x is not None else self.xcor(), y if y is not None else self.ycor())
    self.pendown()
    for i in range(sides):
      self.forward(length)
      self.right(360/sides)
    self.penup()
    self.hideturtle()

This really took some work to get right. At first, I wrote this so that the user needed to specify a goto() location to begin drawing, but that felt wrong. I knew I was going to add a parameter that instantiated the class at a specific location. Given that, it only seemed appropriate that draw_polygon would draw in place unless otherwise specified.

The first thing I tried was using self.xcor() as a default value for the x argument. However, that threw an error. After looking into it, that’s apparently a no-no. Python won’t let you include self method calls as default arguments, because the defaults are evaluated when the method is defined and self can change between then and being called. So, I found the solution to set the default to None, then using an if statement in the method definition to set the value to self.xcor().

That was the only real hurdle in this exercise. I had already written the draw_polygon function for an earlier exercise, so I just included it as a new method. Then, I created four new NinjaTurtles, named Leonardo, Raphael, Donatello, and Michelangelo.

The complete trinket can be found below: