Question

I’m receiving this error in my Django application, however, it only happens once a day or less and it’s proving extremely difficult to debug.

Environment:

Request Method: POST

Django Version: 1.3.1
Python Version: 2.6.6
Installed Applications:
['django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.sites',
 'fimedlabs',
 'data',
 'djcelery']
Installed Middleware:
('django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'fimedlabs.auth.userMiddleWare')


Traceback:
File "/usr/local/lib/python2.6/dist-packages/django/core/handlers/base.py" in get_response
  178.                 response = middleware_method(request, response)
File "/usr/local/lib/python2.6/dist-packages/django/contrib/sessions/middleware.py" in process_response
  36.                 request.session.save()
File "/usr/local/lib/python2.6/dist-packages/django/contrib/sessions/backends/db.py" in save
  57.             session_data = self.encode(self._get_session(no_load=must_create)),
File "/usr/local/lib/python2.6/dist-packages/django/contrib/sessions/backends/base.py" in encode
  93.         pickled = pickle.dumps(session_dict, pickle.HIGHEST_PROTOCOL)

Exception Type: PicklingError at /
Exception Value: Can't pickle <type 'function'>: attribute lookup __builtin__.function failed

I’ve tried the answer to this:

How to tell for which object attribute pickle fails?

by adding self to the actual error to see if that would print anything in the Django error to no avail.

Where can I print out the object that is giving issues from this error so that it will appear in the Django error page?

Thanks!
~Matt

EDIT: The only object I’m storing in the cache, is a user object with the code:

class user(object):
username = str()
userid = uuid.UUID(int=0)

client = models.Client()
clientid = uuid.UUID(int=0)
clientname = ''

data = models.User()
accesslevel = models.AccessLevel()

active = False
client_active = False
isFimed = False
isFimedAdmin = False
isClientAdmin = False
isFimedManager = False
mysettingsform = None
viewingas = False

menu = []

_exists = False
_authenticated = False

def __str__(self):
    return str(self.__dict__.copy())

def __getstate__(self):
    return self.__dict__.copy()

def __setstate__(self, dict):
    self.__dict__ = dict

def __init__(self, username=None):
    if username:
        self.initialize(username)

def initialize(self, username):
    self.username = username
    model = models.User.objects.filter(username=username).all()
    if len(model) == 1:
        model = model[0]
        self.data = model
        self._exists = True
        self.userid = self.data.id
        self.active = self.data.active
        self.isFimed = self.data.isFimed()
        self.isFimedAdmin = self.data.isFimedAdmin()
        self.isClientAdmin = self.data.isClientAdmin()
        self.isFimedManager = self.data.isFimedManager()
        self.mysettingsform = UserFormSelf(initial={"id":model.id, "username":model.username, "name":model.name, "email":model.email, "phone":model.phone})

        self.accesslevel = models.AccessLevel.objects.filter(id=self.data.accesslevel_id)[:1][0].level
        cli = self.data.client
        self.client = cli
        self.clientid = cli.id
        self.clientname = cli.name
        if cli.active:
            self.client_active = True

        model.lastlogin = datetime.datetime.now()
        model.save()

        self.menu = getMenu(self.data)
    else:
        self._exists = False

def authenticate(self, password):
    self._authenticated = False
    if (self.active == False or self.client_active == False):
        return False
    if self._exists:
        import hashlib
        hash = hashlib.md5('%s%s' % (str(password), self.data.pwsalt)).hexdigest()
        if hash == self.data.pwhash:
            self._authenticated = True
            return True
    return False

def updateUser(self):
    self.initialize(models.User.objects.filter(id=self.userid).get().username)

def mkContext(self):
    c = Context()
    c['menu'] = self.menu
    c['user'] = self
    c['language'] = language
    c['colors'] = colors
    c["isFimed"] = self.isFimed
    c["isFimedAdmin"] = self.isFimedAdmin
    c["isClientAdmin"] = self.isClientAdmin
    c["isFimedManager"] = self.isFimedManager
    c["mysettingsform"] = self.mysettingsform
    return c

EDIT: WSGI file after Werkzeug:

import django.core.handlers.wsgi
djangoapplication = django.core.handlers.wsgi.WSGIHandler()
def application(environ, start_response):
    if 'SCRIPT_NAME' in environ:
        del environ['SCRIPT_NAME']
    return djangoapplication(environ, start_response)
# The following lines enable the werkzeug debugger
import django.views.debug
def null_technical_500_response(request, exc_type, exc_value, tb):
    raise exc_type, exc_value, tb
django.views.debug.technical_500_response = null_technical_500_response
from werkzeug.debug import DebuggedApplication
application = DebuggedApplication(application, evalex=True)

Answer 1

Where can I print out the object that is giving issues from this error so that it will appear in the Django error page?

The short answer – without recompiling cPickle, you can’t.

Longer answer: This is the piece of code that raises the exception:

root $ grep -Hra "attribute lookup" /usr/lib64/ 2>/dev/null | grep -a failed
/usr/lib64/python2.7/lib-dynload/cPickle.so:H�H���P0H�5zM H�=1��M��H��H�ZM �����H�=�1�H���M��H��H��M �����H�4M H�5~H���H���������H�M H�5tH���H���������H��L H�5�H���qH�����d���H�M H�5NH���SH�����F���H�dM H�5bH���5H�����(���H�=X1��O��H�HC H�5I H�=U1�A��H��L �vH��H��I�������H���RK��H�=.H����J��H�5$H��H��H�D$�G��H�D$H��tH�H��H��H��gH�DL�ttH�qH�5nH�=kH��1��XK��H�5bH��H��I����F��H�5\L��H���F��H��tH�EH��H��H�E��M�������I�$H��H��I�$�t���I�DL���P0�d���f�H�EH��H��H�E�F���H�H���P0�7���@H�|$H��P0�����H�H���P0�����H�H���P0�k�����UH��SH�H�H: H���tH�;: H���H�H���u�H�[��H��M��H��attribute deletion is not supportedunsupported pickle protocol: %dargument must have 'read' and 'readline' attributespickle protocol %d asked for; the highest available protocol is %dargument must have 'write' attributeGlobal and instance pickles are not supported.Attempt to getvalue() a non-list-based picklerUnexpected data in internal listBINSTRING pickle has negative byte countno int where int expected in memoCan't pickle %s: import of module %s failedCan't pickle %s: attribute lookup %s.%s failedCan't pickle %s: it's not the same object as %s.%sCan't pickle %s: extension code %s isn't an integerCan't pickle %s: extension code %ld is out of rangecould not convert string to intLONG pickle has negative byte countcould not convert string to floatBINUNICODE pickle has negative byte countunregistered extension code %ld_inverted_registry[%ld] isn't a 2-tuple of stringsA load persistent id instruction was encountered,

If you look close enough, there’s a piece that says

Can't pickle %s: attribute lookup %s.%s failed

Now, if you download Python sources, you can easily find the piece of code responsible for raising the exception in the function static int save_global(Picklerobject *self, PyObject *args, PyObject *name) of ./Modules/cPickle.c:

klass = PyObject_GetAttrString(mod, name_str);
if (klass == NULL) {
    cPickle_ErrFormat(PicklingError,
                      "Can't pickle %s: attribute lookup %s.%s "
                      "failed",
                      "OSS", args, module, global_name);
    goto finally;
}

So, the best you can do to debug this error is to format the string differently (probably providing PyString_AS_STRING((PyStringObject *)name), recompile and install the modified version of Python.

Yeah, I know that’s too bad. I just had the same problem myself.