Extreme Yaro weirdness

[Ron Garret]

I'm running the following WSGI app under Yaro:

def error(req):
  try:
    req.non_existent_key
  except:
    try:
      return cgitb.html(sys.exc_info())
    except:
      return 'foo'

The result of running this is 'foo'.  In other words, the reference to 
the non-existent key generates an exception as expected, but then the 
generation of the traceback generates ANOTHER exception, which I would 
not have expected.  If I add another TRY/EXCEPT block to capture this 
exception, the result is attached at the bottom of this message.

It gets better.

I get the same result whether I run under Apache/mod_wsgi or standalone 
using wsgi_ref.  But if I add the following code to try to capture a 
Yaro request object so I can noodle around with it:


def error(req):
  global req1
  req1=req
  try: ...


it makes the problem go away!  But it ONLY makes the problem go away 
when running under wsgi_ref, not under Apache!

The problem seems to be specific to Yaro.  If I make an instance of an 
object and try to dereference a non-existent attribute, the initial 
traceback gets generated with no problem.  Also, the Yaro code for 
Request.__getattr__ ultimately calls req.__dict__[attr].  If I make this 
call directly, the problem also goes away.

I am quite baffled by this.  Any suggestions on how to debug this would 
be much appreciated.

Thanks,
rg


----


<type 'exceptions.KeyError'>
Python 2.5: /usr/local/bin/python
Mon Feb  2 00:54:33 2009

A problem occurred in a Python script.  Here is the sequence of
function calls leading up to the error, in the order they occurred.

 /www/sites/mcia.cc/files/wsgi/test.wsgi in error(req=<yaro.Request 
object at 0x2aaaab94a690>)
  212   except:
  213     try:
  214       return cgitb.text(sys.exc_info())
  215     except:
  216       try:
global cgitb = <module 'cgitb' from '/usr/lib/python2.5/cgitb.pyc'>
cgitb.text = <function text at 0x2aaaab0adc80>
global sys = <module 'sys' (built-in)>
sys.exc_info = <built-in function exc_info>

 /www/sites/cgitb.py in text((etype=<type 'exceptions.KeyError'>, 
evalue=KeyError('non_existent_key',), etb=<traceback object at 
0x2aaaab960368>), context=5)
  215             try: return linecache.getline(file, lnum[0])
  216             finally: lnum[0] += 1
  217         vars = scanvars(reader, frame, locals)
  218 
  219         rows = [' %s %s' % (file, call)]
builtinvars = <built-in function vars>
global scanvars = <function scanvars at 0x2aaaab0adb90>
reader = <function reader at 0x2aaaabbbea28>
frame = <frame object at 0xba49e0>
locals = {'req': <yaro.Request object at 0x2aaaab94a690>}

 /www/sites/cgitb.py in scanvars(reader=<function reader at 
0x2aaaabbbea28>, frame=<frame object at 0xba49e0>, locals={'req': 
<yaro.Request object at 0x2aaaab94a690>})
   82             if lasttoken == '.':
   83                 if parent is not __UNDEF__:
   84                     value = getattr(parent, token, __UNDEF__)
   85                     vars.append((prefix + token, prefix, value))
   86             else:
value = <yaro.Request object at 0x2aaaab94a690>
builtingetattr = <built-in function getattr>
parent = <yaro.Request object at 0x2aaaab94a690>
token = 'non_existent_key'
__UNDEF__ undefined

 /www/sites/mcia.cc/files/wsgi/yaro.py in __getattr__(self=<yaro.Request 
object at 0x2aaaab94a690>, attr='non_existent_key')
  215         elif attr == 'cookie' and not 'cookie' in self.__dict__:
  216             self._load_cookie()
  217         return self.__dict__[attr]
  218 
  219     def _parse_query(self):
self = <yaro.Request object at 0x2aaaab94a690>
self.__dict__ = {'_start_response': <built-in method start_response of 
mod_wsgi.Adapter object at 0x2aaaaab218a0>, 'content_length': '', 
'content_type': '', 'environ': {'DOCUMENT_ROOT': 
'/www/sites/mcia.cc/html', 'GATEWAY_INTERFACE': 'CGI/1.1', 
'HTTP_ACCEPT': 
'text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plai
n;q=0.8,image/png,*/*;q=0.5', 'HTTP_ACCEPT_ENCODING': 'gzip, deflate', 
'HTTP_ACCEPT_LANGUAGE': 'en-us', 'HTTP_CACHE_CONTROL': 'max-age=0', 
'HTTP_CONNECTION': 'keep-alive', 'HTTP_COOKIE': 'sid=55UGS64T', 
'HTTP_HOST': 'mcia.cc', 'HTTP_REFERER': 'http://mcia.cc/wtest/menu', 
...}, 'exc_info': None, 'extra_props': None, 'method': 'GET', 'query': 
{}, 'res': <yaro.Response object at 0x2aaaab94a710>, 
'start_response_called': False, ...}
attr = 'non_existent_key'
<type 'exceptions.KeyError'>: 'non_existent_key'

The above is a description of an error in a Python program.  Here is
the original traceback:

Traceback (most recent call last):
  File "/www/sites/mcia.cc/files/wsgi/test.wsgi", line 214, in error
    return cgitb.text(sys.exc_info())
  File "cgitb.py", line 217, in text
    vars = scanvars(reader, frame, locals)
  File "cgitb.py", line 84, in scanvars
    value = getattr(parent, token, __UNDEF__)
  File "/www/sites/mcia.cc/files/wsgi/yaro.py", line 217, in __getattr__
    return self.__dict__[attr]
KeyError: 'non_existent_key'