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<TITLE>13: Projects</TITLE>
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Thinking in Python<br>
<small>Revision 0.1.2 (12/31/01) -- Incomplete and Unfinished</small></FONT></H2>
<H3><FONT FACE="Verdana, Tahoma, Arial, Helvetica, Sans">
by Bruce Eckel ©2002 MindView, Inc.</FONT></H3>
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</P></DIV><A NAME="_Toc534420148"></A><A NAME="Heading99"></A><FONT FACE = "Verdana, Tahoma, Arial, Helvetica, Sans"><H1 ALIGN="LEFT">
13: Projects</H1></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia" SIZE=4 COLOR="Red">This chapter has not
had any significant translation yet.</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia" SIZE=4>A number of more challenging
projects for you to solve. [[Some of these may turn into examples in the book,
and so at some point might disappear from here]]
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_459">Add Comment</A></FONT><A NAME="_Toc534420149"></A><BR></P></DIV>
<A NAME="Heading100"></A><FONT FACE = "Verdana, Tahoma, Arial, Helvetica, Sans"><H2 ALIGN="LEFT">
Rats & Mazes</H2></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">First, create a <I>Blackboard</I> (cite
reference) which is an object on which anyone may record information. This
particular blackboard draws a maze, and is used as information comes back about
the structure of a maze from the rats that are investigating it.
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_460">Add Comment</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Now create the maze itself. Like a real
maze, this object reveals very little information about itself — given a
coordinate, it will tell you whether there are walls or spaces in the four
directions immediately surrounding that coordinate, but no more. For starters,
read the maze in from a text file but consider hunting on the internet for a
maze-generating algorithm. In any event, the result should be an object that,
given a maze coordinate, will report walls and spaces around that coordinate.
Also, you must be able to ask it for an entry point to the maze.
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_461">Add Comment</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Finally, create the maze-investigating
<B>Rat</B> class. Each rat can communicate with both the blackboard to give the
current information and the maze to request new information based on the current
position of the rat. However, each time a rat reaches a decision point where the
maze branches, it creates a new rat to go down each of the branches. Each rat is
driven by its own thread. When a rat reaches a dead end, it terminates itself
after reporting the results of its final investigation to the blackboard.
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_462">Add Comment</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The goal is to completely map the maze,
but you must also determine whether the end condition will be naturally found or
whether the blackboard must be responsible for the decision.
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_463">Add Comment</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">An example implementation by Jeremy
Meyer:</FONT><BR></P></DIV>
<BLOCKQUOTE><FONT SIZE = "+1"><PRE># c13:Maze.py
<font color=#0000ff>class</font> Maze(Canvas):
private Vector lines # a line <font color=#0000ff>is</font> a char array
private int width = -1
private int height = -1
public static void main (String [] args)
throws IOException:
<font color=#0000ff>if</font> (args.length < 1):
<font color=#0000ff>print</font> “Enter filename“
System.exit(0)
Maze m = Maze()
m.load(args[0])
Frame f = Frame()
f.setSize(m.width*20, m.height*20)
f.add(m)
Rat r = Rat(m, 0, 0)
f.setVisible(1)
<font color=#0000ff>def</font> __init__(self):
lines = Vector()
setBackground(Color.lightGray)
synchronized public boolean
isEmptyXY(int x, int y):
<font color=#0000ff>if</font> (x < 0) x += width
<font color=#0000ff>if</font> (y < 0) y += height
# Use mod arithmetic to bring rat <font color=#0000ff>in</font> line:
byte[] by =
(byte[])(lines.elementAt(y%height))
<font color=#0000ff>return</font> by[x%width]==' '
synchronized public void
setXY(int x, int y, byte newByte):
<font color=#0000ff>if</font> (x < 0) x += width
<font color=#0000ff>if</font> (y < 0) y += height
byte[] by =
(byte[])(lines.elementAt(y%height))
by[x%width] = newByte
repaint()
public void
load(String filename) throws IOException:
String currentLine = null
BufferedReader br = BufferedReader(
FileReader(filename))
<font color=#0000ff>for</font>(currentLine = br.readLine()
currentLine != null
currentLine = br.readLine()) :
lines.addElement(currentLine.getBytes())
<font color=#0000ff>if</font>(width < 0 ||
currentLine.getBytes().length > width)
width = currentLine.getBytes().length
height = len(lines)
br.close()
<font color=#0000ff>def</font> update(self, Graphics g): paint(g)
public void paint (Graphics g):
int canvasHeight = self.getBounds().height
int canvasWidth = self.getBounds().width
<font color=#0000ff>if</font> (height < 1 || width < 1)
<font color=#0000ff>return</font> # nothing to do
int width =
((byte[])(lines.elementAt(0))).length
<font color=#0000ff>for</font> (int y = 0 y < len(lines) y++):
byte[] b
b = (byte[])(lines.elementAt(y))
<font color=#0000ff>for</font> (int x = 0 x < width x++):
switch(b[x]):
case ' ': # empty part of maze
g.setColor(Color.lightGray)
g.fillRect(
x*(canvasWidth/width),
y*(canvasHeight/height),
canvasWidth/width,
canvasHeight/height)
<font color=#0000ff>break</font>
case '*': # a wall
g.setColor(Color.darkGray)
g.fillRect(
x*(canvasWidth/width),
y*(canvasHeight/height),
(canvasWidth/width)-1,
(canvasHeight/height)-1)
<font color=#0000ff>break</font>
default: # must be rat
g.setColor(Color.red)
g.fillOval(x*(canvasWidth/width),
y*(canvasHeight/height),
canvasWidth/width,
canvasHeight/height)
<font color=#0000ff>break</font>
# :~</PRE></FONT></BLOCKQUOTE>
<BLOCKQUOTE><FONT SIZE = "+1"><PRE># c13:Rat.py
<font color=#0000ff>class</font> Rat:
static int ratCount = 0
private Maze prison
private int vertDir = 0
private int horizDir = 0
private int x,y
private int myRatNo = 0
<font color=#0000ff>def</font> __init__(self, Maze maze, int xStart, int yStart):
myRatNo = ratCount++
<font color=#0000ff>print</font> (<font color=#004488>"Rat no."</font> + myRatNo +
<font color=#004488>" ready to scurry."</font>)
prison = maze
x = xStart
y = yStart
prison.setXY(x,y, (byte)'R')
Thread():
<font color=#0000ff>def</font> run(self){ scurry()
.start()
<font color=#0000ff>def</font> scurry(self):
# Try <font color=#0000ff>and</font> maintain direction <font color=#0000ff>if</font> possible.
# Horizontal backward
boolean ratCanMove = 1
<font color=#0000ff>while</font>(ratCanMove):
ratCanMove = 0
# South
<font color=#0000ff>if</font> (prison.isEmptyXY(x, y + 1)):
vertDir = 1 horizDir = 0
ratCanMove = 1
# North
<font color=#0000ff>if</font> (prison.isEmptyXY(x, y - 1))
<font color=#0000ff>if</font> (ratCanMove)
Rat(prison, x, y-1)
# Rat can move already, so give
# this choice to the next rat.
<font color=#0000ff>else</font>:
vertDir = -1 horizDir = 0
ratCanMove = 1
# West
<font color=#0000ff>if</font> (prison.isEmptyXY(x-1, y))
<font color=#0000ff>if</font> (ratCanMove)
Rat(prison, x-1, y)
# Rat can move already, so give
# this choice to the next rat.
<font color=#0000ff>else</font>:
vertDir = 0 horizDir = -1
ratCanMove = 1
# East
<font color=#0000ff>if</font> (prison.isEmptyXY(x+1, y))
<font color=#0000ff>if</font> (ratCanMove)
Rat(prison, x+1, y)
# Rat can move already, so give
# this choice to the next rat.
<font color=#0000ff>else</font>:
vertDir = 0 horizDir = 1
ratCanMove = 1
<font color=#0000ff>if</font> (ratCanMove): # Move original rat.
x += horizDir
y += vertDir
prison.setXY(x,y,(byte)'R')
# If <font color=#0000ff>not</font> then the rat will die.
<font color=#0000ff>try</font>:
Thread.sleep(2000)
catch(InterruptedException ie):
<font color=#0000ff>print</font> (<font color=#004488>"Rat no."</font> + myRatNo +
<font color=#004488>" can't move..dying..aarrgggh."</font>)
# :~</PRE></FONT></BLOCKQUOTE><DIV ALIGN="LEFT"><P><FONT FACE="Georgia">The maze initialization file:
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_464">Add Comment</A></FONT><BR></P></DIV>
<BLOCKQUOTE><FONT SIZE = "+1"><PRE>#:! c13:Amaze.txt
* ** * * ** *
*** * ******* * ****
*** ***
***** ********** *****
* * * * ** ** * * * ** *
* * * * ** * * * * **
* ** * **
* ** * ** * ** * **
*** * *** ***** * *** **
* * * * * *
* ** * * * ** * *
# :~</PRE></FONT></BLOCKQUOTE><DIV ALIGN="LEFT"><P><A NAME="_Toc534420150"></A><BR></P></DIV>
<A NAME="Heading101"></A><FONT FACE = "Verdana, Tahoma, Arial, Helvetica, Sans"><H3 ALIGN="LEFT">
Other maze resources</H3></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">A discussion of algorithms to create
mazes as well as Java source code to implement them:
<A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_465">Add Comment</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><A HREF="http://www.mazeworks.com/mazegen/mazegen.htm">http://www.mazeworks.com/mazegen/mazegen.htm</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">A discussion of algorithms for collision
detection and other individual/group moving behavior for autonomous physical
objects:</FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia"><A HREF="http://www.red3d.com/cwr/steer/">http://www.red3d.com/cwr/steer/</A></FONT><BR></P></DIV>
<DIV ALIGN="LEFT"><P><A NAME="_Toc534420151"></A><BR></P></DIV>
<A NAME="Heading102"></A><FONT FACE = "Verdana, Tahoma, Arial, Helvetica, Sans"><H2 ALIGN="LEFT">
XML Decorator</H2></FONT>
<DIV ALIGN="LEFT"><P><FONT FACE="Georgia">Create a pair of decorators for I/O
Readers and Writers that encode (for the Writer decorator) and decode (for the
reader decorator)
XML</FONT><FONT FACE="Georgia"><A HREF="http://www.mindview.net/Books/TIPython/BackTalk/FindPage/A_466">Add Comment</A></FONT><BR></P></DIV>
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