[Zope] Storing callable references in the ZODB

2 Nov 2004

      I recently discovered that the ZODB (possibly newly, or 
maybe I just haven't noticed this problem before) will not
allow a persistent instance to have an attribute assigned
to it which is a function or a method.

In other words, the following is not allowed:

class MyZopeObj(Persistent,...):
     def __init__(self, callme=None):
 	self.func = callme

although you can do this:

class MyZopeObj(Persistent,...):
     callme = ...

(e.g. archived message 
http://gossamer-threads.com/lists/zope/users/168215 )

I have a situation in which I need to find a way to
reference a callable object (doesn't strictly have to
be a method/function, but I do want to call it), and
I'm having a little difficulty getting it to fail for
me so that I can test some workaround ideas I have.

Here's what I'm doing so far. I'm using Python 2.3.4
and Zope 2.7.0:

import Zope
Zope.configure('/location/of/zope.conf')
app = Zope.app()
app.objectIds()
# This displays the contents of my root folder in my
# local Zope instance.  So far so good.

# make a sandbox folder to play with
app.manage_addFolder('test_perscall')
f = app.test_perscall

# define a function to evilly reference from ZODB:
def spam(a):
    return a

# OK, why doesn't *this* fail?
f.spam = spam

#(Surely this is storing the function
# reference in the ZODB?)

# Maybe I need to specifically init this reference in
# a persistent object?  Let's try that . . .

from Persistence import Persistent
from OFS import Folder

class WCall(Persistent, Folder):
    """
    Test object to hold a method in it's instance.
    """
    def __init__(self, id, title=''):
        self.id = id
        self.title = title
        self.spam = spam

ob = WCall('wcall', 'Test callable object instance method')
f._setOb('wcall', ob)

# WHAT?! *Still* no failure?

I figure I must need to get a ZODB commit to happen or 
something to make my "unpickleable" error come up, but
how do I make that happen from the Python interpreter
command line?

Any comments would be much appreciated.  What I need to
do is get the error to come up reliably so that I know
I understand its limits, and then I need to test my
workaround (which is to trace the function's module
and name, store the result in a persistent callable
object wrapper which can retrieve the function and
call it at need).  And of course, I have to make it work
without error for my workaround code.

TIA & Cheers,
Terry

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com