Stupefying Django error

Wow. I spent a lot of time on this this afternoon. I had a Django application with an admin interface. Every time I tried to create an object with no foreign keys, I got this error on the save:

Traceback (most recent call last):

  File "C:\Python26\lib\site-packages\django\core\servers\basehttp.py", line 279, in run
    self.result = application(self.environ, self.start_response)

  File "C:\Python26\lib\site-packages\django\core\servers\basehttp.py", line 651, in __call__
    return self.application(environ, start_response)

  File "C:\Python26\lib\site-packages\django\core\handlers\wsgi.py", line 241, in __call__
    response = self.get_response(request)

  File "C:\Python26\lib\site-packages\django\core\handlers\base.py", line 134, in get_response
    return self.handle_uncaught_exception(request, resolver, exc_info)

  File "C:\Python26\lib\site-packages\django\core\handlers\base.py", line 154, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)

  File "C:\Python26\lib\site-packages\django\views\debug.py", line 40, in technical_500_response
    html = reporter.get_traceback_html()

  File "C:\Python26\lib\site-packages\django\views\debug.py", line 86, in get_traceback_html
    frames = self.get_traceback_frames()

  File "C:\Python26\lib\site-packages\django\views\debug.py", line 205, in get_traceback_frames
    pre_context_lineno, pre_context, context_line, post_context = self._get_lines_from_file(filename, lineno, 7, loader, module_name)

  File "C:\Python26\lib\site-packages\django\views\debug.py", line 186, in _get_lines_from_file
    context_line = source[lineno].strip('\n')

IndexError: list index out of range

Totally mysterious: there is not a line of my code in the trace stack and I have no idea what file it is trying to index into. I really made no progress on this until I tried the shell:

>>> from django_league.league.models import *
>>> Sport.objects.create(sport_name='Hockey')
__unicode__
Traceback (most recent call last):
  File "lgt;console>", line 1, in lgt;module>
  File "C:\Python26\lib\site-packages\django\db\models\base.py", line 328, in __
repr__
    u = unicode(self)
  File "C:\Users\hughdbrown\Documents\django\django_league\..\django_league\leag
ue\models.py", line 17, in __unicode__
    return u"%s" % (sport_name, )
NameError: global name 'sport_name' is not defined

Now we're getting somewhere, I thought. I have a function of mine in scope. The problem was that I had defined my __unicode__ method without using self in the code:

class Sport(models.Model):    
    sport_name = models.CharField(max_length=20)
    def __unicode__(self):
        return u"%s" % (self.sport_name, )

    @models.permalink
    def get_absolute_url(self):
        return ('sport', None, {'object_id' : self.id})

    class Meta:
        ordering = ['sport_name']

So fixing it was pretty easy once I knew that.