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  <h1>Debugging Lab</h1>

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  <p>This assignment is intended to give you a chance to demonstrate that you know how to step through code 
  and verfiy code execution.  Use the method described in Chapter 4 from 
  <a href="/courses/cs190/2007/documents/restricted/Writing%20Solid%20Code.pdf">Writing Solid Code</a>.</p>

  <ol>
    <li>Download the <a href="pymine.tar">Minesweeper source</a> and decompress it (<code>tar -xvf 
    pymine.tar</code>).</li>
    <li>Re-read Maguire's description of how to step through code.</li>
    <li>Set up to record your debugging session, probably using cut-and-paste.</li>
    <li>Take a look at the documentation for the <a
    href="http://docs.python.org/lib/module-pdb.html">pdb</a> Python module.
    It's very similar to gdb for C and C++ programs, so if you're familiar with
    that you should feel right at home in pdb.</li>
    <li>Step through the method <code>MineField.populate</code> in the debugger (this method is called every 
    time you start a new game, after selecting the field size).  Follow the guidelines from <em>Writing Solid 
    Code</em> chapter 4 on how to do this.  Check variable values and other state information before and after 
    execution of each line and verify that the line did what it should.  Be sure to step through <em>all</em> 
    the lines of code, even if that means fixing some of the errors as you go along.  (It is only necessary to 
    step through the populate function and not the subfunctions called by it.)</li>
    <li>Add concise comments to your transcript explaining what bugs you found and how you fixed them.</li>
    <li>Hand in your debugger transcript.</li>
  </ol>

  <p>The rubric for this assignment is available <a href="rubrics/DebuggingRubric.doc">here</a>.</p>

  <h2>How does this help me with the chosen project framework, TurboGears?</h2>

  <p>You can use pdb within TurboGears.  To do so, open up the start-....py file
  used to run the project and add the following lines of code right before
  the last line which starts the server:</p>
  <pre>import pdb
cherrypy.config.update({'autoreload.on': False})
pdb.set_trace()</pre>
  <p>
  This does a couple things.  First, it loads pdb.  Second, it disables
  auto-detection of changes to files while the server is running - without this,
  if you change a file, the server will restart but the debugger won't quite
  work...  Finally the set_trace() gives you an initial pdb prompt from which
  you can set breakpoints in your code.  For example, setting a breakpoint in
  the TurboGears wiki tutorial code:
  </p>
  <pre>[colin@sliver:~/Desktop/wiki20]$ python start-wiki20.py 
> /home/colin/Desktop/wiki20/start-wiki20.py(32)<module>()
-> turbogears.start_server(Root())
(Pdb) b wiki20/controllers.py:25
Breakpoint 1 at /home/colin/Desktop/wiki20/wiki20/controllers.py:25
(Pdb) </pre>
  <p>Try it out now if you have time!</p>

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