It seems like the best approach, for my app at least, is to define a
decorator to handle the serializing and unserializing of objects
stored in session, e.g.
@sessionobjects
def mycontroller():
...
This seems to be working, but I'm wondering if it has any known
gotchas relative to the under-the-hood workings of web2py. For
example, will the session always remain unserialized until after the
view is rendered? Or within the context of a redirect?
If this implementation seems sound, I'll post it in a comment to the
sessions page of the online doc.
Here's the code for the decorator.
## -----------------------------------------------------
def sessionobjects(f):
"""
Web2py sessions can't store app-defined objects unless they are
pre-serialized.
This decorator ensures that a list of session member objects are
unserialized before use and re-serialized afterward.
It also serves as a default initializer for the members, setting
them to None if they don't exist.
"""
def new_f():
objnames = ["problem",] ## edit list to fit your app
for n in objnames:
## In normal python, you would use hasattr() to see
## if the member exists, but session is of class Storage
## which returns None if the member doesn't exist.
if None != getattr(session,n):
setattr(session,n,cPickle.loads(getattr(session,n)))
try:
return f()
finally:
for n in objnames:
setattr(session,n,cPickle.dumps(getattr(session,n)))
return new_f
## -----------------------------------------------------
On May 6, 5:59 pm, mdipierro <[email protected]> wrote:
> yes.
>
> On May 6, 3:58 pm, MikeEllis <[email protected]> wrote:
>
> > Thanks, Massimo. Makes perfect sense now that you've explained it.
> > The nature of my app is such that I really do need to keep the object
> > in the session, so just to make sure I understand, I need to do
> > something like
>
> > session.problem = cPickle.dumps(problem)
>
> > before leaving any function that alters the object, and
>
> > problem = cPickle.loads(session.problem)
>
> > on entry to any function that needs to use it?
>
> > Cheers,
> > Mike
>
> > On May 6, 4:31 pm, mdipierro <[email protected]> wrote:
>
> > > in web2py you CANNOT store an object into a session unless you store
> > > it already serialized. This is because the session is retrieved before
> > > your code is executed and therefore before the module in question is
> > > imported.
>
> > > On May 6, 3:03 pm, MikeEllis <[email protected]> wrote:
>
> > > > Oops forgot to include "import os" in my example code. It was imported
> > > > elsewhere in my app. With that correction, I have now reproduced the
> > > > problem in a new app containing nothing but the example code.
>
> > > > I've tried googling the PicklingError message and found some
> > > > references to problems under WSGI, but they seemed to be GAE related
> > > > and the explanations weren't very clear (or at least not easy to
> > > > understand :-)
>
> > > > Any help much appreciated,
> > > > Mike
>
> > > > On May 6, 2:34 pm, MikeEllis <[email protected]> wrote:
>
> > > > > More info:
>
> > > > > I've confirmed that any class defined in the modules directory can
> > > > > reproduce the problem. To verify, create a new module named
> > > > > "dummyclass.py" containing
>
> > > > > import uuid
> > > > > class Problem(object):
> > > > > """ Just to validate that session.problem pickling error
> > > > > is not related to anything in PTProblem class.
>
> > > > > """
> > > > > def __init__(self,description,ownerid=0):
> > > > > self.uuid = uuid.uuid1()
>
> > > > > and alter the local_import statement in my previous post to look like:
>
> > > > > PTProblemClass = local_import('dummyclass',reload=True)
>
> > > > > Thanks,
> > > > > Mike
>
> > > > > On May 6, 2:07 pm, MikeEllis <[email protected]> wrote:
>
> > > > > > The class isn't really named Foo, of course, but it makes for a more
> > > > > > readable subject line.
>
> > > > > > Here's the actual ticket:
>
> > > > > > Traceback (most recent call last):
> > > > > > File "/Users/mellis/web2py/gluon/main.py", line 504, in wsgibase
> > > > > > session._try_store_on_disk(request, response)
> > > > > > File "/Users/mellis/web2py/gluon/globals.py", line 375, in
> > > > > > _try_store_on_disk
> > > > > > cPickle.dump(dict(self), response.session_file)
> > > > > > PicklingError: Can't pickle <class
> > > > > > 'applications.peertool.modules.PTProblemClass.Problem'>: it's not
> > > > > > the
> > > > > > same object as applications.peertool.modules.PTProblemClass.Problem
>
> > > > > > And here is a simple default.py that reliably reproduces the error:
>
> > > > > > import cPickle
> > > > > > PTProblemClass = local_import('PTProblemClass',reload=True)
>
> > > > > > def mytest():
>
> > > > > > ## Create an instance of class Problem and prove that it
> > > > > > ## can be pickled.
> > > > > > problem = PTProblemClass.Problem("Just testing ...",ownerid=2)
> > > > > > filename = 'problem_' + str(problem.uuid)
> > > > > > PROBLEMFILEPATH =
> > > > > > os.path.join('applications','peertool','private')
> > > > > > f = open(os.path.join(PROBLEMFILEPATH,filename),'w')
> > > > > > cPickle.dump(problem,f)
> > > > > > f.close()
>
> > > > > > ## Assign to session.problem and show that it is
> > > > > > ## an instance of the class
> > > > > > session.problem = problem
> > > > > > assert isinstance(session.problem, PTProblemClass.Problem)
>
> > > > > > ## Return a message of comfort and cheer
> > > > > > return dict(message=T("Test completed"))
>
> > > > > > def index(): ## Unaltered from new app creation
> > > > > > """
> > > > > > example action using the internationalization operator T and
> > > > > > flash
> > > > > > rendered by views/default/index.html or views/generic.html
> > > > > > """
> > > > > > response.flash = T('Welcome to web2py')
> > > > > > return dict(message=T('Hello World'))
>
> > > > > > I've not included the Problem class code. It's proprietary and I'm
> > > > > > reasonably convinced its not part of the problem since there are no
> > > > > > problems pickling (or unpickling) instances of it.
>
> > > > > > I can reproduce the problem by the following steps:
> > > > > > 1. Visit the index page, no ticket.
> > > > > > 2. Visit mytest, no ticket
> > > > > > 3. Visit index page again, get the ticket.
>
> > > > > > I'm running web2py 1.74.9.
>
> > > > > > Anyone know how to solve this? It's a particularly annoying because
> > > > > > once the error occurs, the entire app is hosed until I visit the
> > > > > > site
> > > > > > page and clean the sessions and caches.
>
> > > > > > Thanks,
> > > > > > Mike
>
>
