This time I will try to get all the comments in one submission... Looking at the page you uploaded today:
The typical example page refers to self.request, I think that should just be request with def edit(request):, etc.
session wasn't imported (assuming a DBSession?):
item = session.query(MyModel).get(item_id)
Also, looks like you need to have sessions enabled for the CSRF to work, might be worth a mention?
After fixing these the demo ran (at least add, it's bedtime and I haven't figured out edit yet), though:
if form.validate(): never seemed to be true?
PS Is there a reason the only "Type" option is "bug" on the submit form for Bitbucket?