id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
9608	Broken model unicode methods can lead to bare exceptions	Karen Tracey	nobody	"Given this model registerd with the admin:

{{{
# -*- coding: utf-8 -*-
from django.db import models

class BrokenUnicodeMethod(models.Model):
    name = models.CharField(max_length=6)
    def __unicode__(self):
        return 'Názov: %s' % self.name

}}}

attempting to add one in the admin (with DEBUG set to True) generates a bare traceback:

{{{
Traceback (most recent call last):

  File ""/home/kmt/django/trunk/django/core/servers/basehttp.py"", line 278, in run
    self.result = application(self.environ, self.start_response)

  File ""/home/kmt/django/trunk/django/core/servers/basehttp.py"", line 635, in __call__
    return self.application(environ, start_response)

  File ""/home/kmt/django/trunk/django/core/handlers/wsgi.py"", line 239, in __call__
    response = self.get_response(request)

  File ""/home/kmt/django/trunk/django/core/handlers/base.py"", line 128, in get_response
    return self.handle_uncaught_exception(request, resolver, exc_info)

  File ""/home/kmt/django/trunk/django/core/handlers/base.py"", line 148, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)

  File ""/home/kmt/django/trunk/django/views/debug.py"", line 39, in technical_500_response
    html = reporter.get_traceback_html()

  File ""/home/kmt/django/trunk/django/views/debug.py"", line 97, in get_traceback_html
    'exception_value': smart_unicode(self.exc_value, errors='replace'),

  File ""/home/kmt/django/trunk/django/utils/encoding.py"", line 35, in smart_unicode
    return force_unicode(s, encoding, strings_only, errors)

  File ""/home/kmt/django/trunk/django/utils/encoding.py"", line 70, in force_unicode
    raise DjangoUnicodeDecodeError(s, *e.args)

DjangoUnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 1: ordinal not in range(128). You passed in DjangoUnicodeDecodeError('ascii', 'N\xc3\xa1zov: ', 1, 2, 'ordinal not in range(128)') (<class 'django.utils.encoding.DjangoUnicodeDecodeError'>)

}}}

The original !DjanoUnicodeDecodeError comes from the admin trying a force_unicode on the new object for the log message.  That gets caught and `get_traceback_html` attempts to calls `smart_unicode` on the exception value, which ultimately calls the `__str__` method for !DjangoUnicodeDecodeError:

{{{
    def __str__(self):
        original = UnicodeDecodeError.__str__(self)
        return '%s. You passed in %r (%s)' % (original, self.obj,
                type(self.obj))
}}}

`self.obj` is the origin object where `__unicode__` generated an exception.  But the attempt to use its repr is going to call unicode on it again, since `__repr__` for an model is (from django/db/models/base.py):

{{{
    def __repr__(self):
        return smart_str(u'<%s: %s>' % (self.__class__.__name__, unicode(self)))
}}}

and we get another !UnicodeDecodeException.

Of course the model's `__unicode__` method is broken, returning non-ASCII data in a bytestring instead of a unicode object, but Django shouldn't obscure that error by generating an error itself trying to say that.  Specifically I think the model `__repr__` ought to guard against `unicode(self)` generating an exception and substitute placeholder text if that happens, but I'm not entirely sure of that so I didn't just do it.  Other opinions?

The original problem was reported in this thread: http://groups.google.com/group/django-users/browse_thread/thread/4209cc8f669f5e12

and involved a `__unicode__` method that looked like this:

{{{
    def __unicode__(self):
        return ""%s %s"" % (self.vrstva, self.nazov)
}}}

Here 'vrstva' is a foreign key, with a valid `__unicode__` method that was returning non-ASCII data, converted to a utf-8 bytestring by the default Model `__str__` method:

{{{
    def __str__(self):
        if hasattr(self, '__unicode__'):
            return force_unicode(self).encode('utf-8')
        return '%s object' % self.__class__.__name__
}}}"		closed	Core (Other)	1.0		fixed			Accepted	0	0	0	0	0	0