newbie, re: tkinter canvas

[Locash]

I have written a script to model Conway's Game of Life.  Currently it
prints successive generations to the console.  But I now want to wrap
it in a GUI.  So far I have created a canvas and populated it with
images of 'dead' cells.  Then the user picks which cells to bring to
life in the initial generation.  Graphically this code does what I
want, but in addition I want to store the information about the cells
status (alive or dead) to a list using the values 1 or 0.  At the
moment, the image that exists in a cell is being stored (imgL or
imgD).

When I make the following changes, suddenly every pick I make wipes
all other images from the canvas.  Can anyone explain to me why this
happens?

I want to change:

"self.emptyWorld[x].append(imgD)" to "self.emptyWorld[x].append(0)"

and

"self.currentGen[i][j] = imgL" to "self.currentGen[i][j] = 1"

~~~~~~~~~~~~~~~~~~~~~~~~~~~
from Tkinter import *

class Application(Frame):
    
    emptyWorld = []
    currentGen = []
        
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.grid()
        self.createWidgets()
        
    def createWidgets(self):        
            
        imgD = PhotoImage(file='death.gif')
        
        self.world = Canvas (self, height=406, width=406, bg=
"#eeeeee", cursor="hand1")
        self.world.grid (row=0, column=0, columnspan=6)
        self.world.bind ("<Button-1>", self.createLife)
        
        for x in range (0,40):
            self.emptyWorld.append([])
            self.currentGen.append([])
            for y in range (0,40):      
                self.world.create_image(((x+1)*10), ((y+1)*10),
image=imgD)
                self.emptyWorld[x].append(imgD)
                self.currentGen = self.emptyWorld       
        self.world.img=imgD
                
    def createLife(self, event):
        
        imgL = PhotoImage(file='life.gif')
        
        x = int(((event.x + 5)/10))*10
        y = int(((event.y + 5)/10))*10
        
        for i in range (0, len(self.currentGen)):
            for j in range (0, len(self.currentGen[i])):
                if x == (i*10) and y == (j*10):                     
                    self.world.create_image(x, y, image=imgL)
                    self.currentGen[i][j] = imgL                    
                else: pass
        self.world.img = imgL                       
          
app = Application() # Instantiate the application class
app.master.title("Conway's Game of Life")
app.mainloop() # Wait for events
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks in advance for your help!