Chapter 13 -- Etch

Well here it is, the first bug report I've received from a reader. Thanks to Gregor Lingl (The same guy who wrote the excellent xturtle module that we based cTurtle on).

Listing 13.4 is wrong. Listing 13.4 provides a class that inherits from Turtle and provides simple onKey callbacks for turning left, right, forward and backward. These callbacks should turn a default amount or go back or forward a default number of spaces.

To avoid a crazy recursion the callbacks were named left5 and right5 in the working version of the code, but somehow the 5 got left off in the published listing.

Here's a complete, tested and working version of listing 13.4

import sys
import os
from cTurtle import Turtle, mainloop

class Etch(Turtle):
    defaultDist = 5
    def __init__(self):
        super(Etch, self).__init__()
        self.color('blue')
        self.pensize(2)
        self.speed(0)
        self.distance = 5
        self.turn = 5
        self.onKey(self.forward,"Up")
        self.onKey(self.bkwd,"Down")
        self.onKey(self.left5,"Left")
        self.onKey(self.right5,"Right")
        self.onKey(self.quit,"q")
        self.listen()        
        self.main()

    def forward(self,distance=defaultDist):
        super(Etch,self).forward(distance)

    def bkwd(self):
        self.backward(self.distance)

    def left5(self):
        self.left(self.turn)

    def right5(self):
        self.right(self.turn)

    def quit(self):
        sys.exit()

    def main(self):
        mainloop()

if __name__ == '__main__':
    etch = Etch()