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
1788	sometimes tecnhical_500_response fails	anonymous	Adrian Holovaty	"In django.views.debug.py the following code fails:

        
{{{
pre_context_lineno, pre_context, context_line, post_context = _get_lines_from_file(filename, lineno, 7)
        frames.append({
            'tb': tb,
            'filename': filename,
            'function': function,
            'lineno': lineno + 1,
            'vars': tb.tb_frame.f_locals.items(),
            'id': id(tb),
            'pre_context': pre_context,
            'context_line': context_line,
            'post_context': post_context,
            'pre_context_lineno': pre_context_lineno + 1,
        })
}}}


It fails on 'pre_context_lineno + 1' in case pre_context_lineno is None (cannot apply '+' to None and 1).
This happens when django can't find the source file where the error occurred. To reproduce:

1. In a view, import some module from a directory in your PYTHONPATH, other than the path to django, 
and directory from which web server starts. 
2. Call some method in this module, which raises an exception. Django will not find the source, and produce a backtrace like this:


{{{

Traceback (most recent call last):

  File ""/home/valeriyz/django/django/core/servers/basehttp.py"", line 272, in run
    self.result = application(self.environ, self.start_response)

  File ""/home/valeriyz/django/django/core/servers/basehttp.py"", line 615, in __call__
    return self.application(environ, start_response)

  File ""/home/valeriyz/django/django/core/handlers/wsgi.py"", line 145, in __call__
    response = self.get_response(request.path, request)

  File ""/home/valeriyz/django/django/core/handlers/base.py"", line 100, in get_response
    return self.get_technical_error_response(request)

  File ""/home/valeriyz/django/django/core/handlers/base.py"", line 133, in get_technical_error_response
    return debug.technical_500_response(request, *sys.exc_info())

  File ""/home/valeriyz/django/django/views/debug.py"", line 99, in technical_500_response
    frames.append({

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

}}}
"	defect	closed	Core (Other)		normal	fixed			Unreviewed	0	0	0	0	0	0