There are a number of place in the django codebase that trap Exception and then raise a new exception. This results in less-than-ideal debugging information being presented in the default error page; in particular, the traceback from the original exception is unavailable.
Most recently, I encountered this in the template renderer:
class DebugNodeList(NodeList):
def render_node(self, node, context):
try:
result = node.render(context)
except TemplateSyntaxError, e:
if not hasattr(e, 'source'):
e.source = node.source
raise
except Exception, e:
from sys import exc_info
wrapped = TemplateSyntaxError(u'Caught an exception while rendering: %s' % force_unicode(e, errors='replace'))
wrapped.source = node.source
wrapped.exc_info = exc_info()
raise wrapped
return result
When this wrapped TemplateSyntaxError? is displayed in the default error page, the traceback ends at the 'raise wrapped' line; the only part of the original exception that is available is the message ("'RelatedManager?' object is not iterable" in my current case). This makes the source of the problem more difficult to determine. The traceback in wrapped.exc_info should be displayed in addition to, or instead of, the traceback currently displayed.
This was briefly discussed (exactly 1 year ago) on django-developers. A partial patch was posted.
