[Zope] cPickle.PicklingError in Connection.py when saving reference to a class method

[Grégoire Weber]

Hi people,

I tried to save a method reference to the ZODB (see below at #####). 
The nop method acts as default method to be called in do_something() 
if an other module using the class does not register itself a method.

Zope 2.3.0 (and also 2.2.4) prints the error shown below which I do 
not understand. I'am using Zope under NT4SP6us.

The same error occures in register_method().

Do I do something wrong? 
Or is there a bug in Zope? 
Or is this kind of thing not possible with the ZODB?

Thanks in advance, Greg

P.S.: As it seems my approach is correct (from the python view), as the 
code snipped at the end of the e-mail shows. But if there is somebody 
on the list who knows a better solution, please let me know!

#------------------------- code fragment -------------------------
import Globals
from Globals import Persistent, Acquisition
import AccessControl
import OFS

class Calendar(OFS.SimpleItem.SimpleItem):
    """ a calendar object """

    def nop(self, beg, end):
        return ''

    def __init__(self, parentFolder, id):
        self.method = self.nop   ##### <-- if I clear this line the error
                                 #####     disappears
        self.id=str(id)
        self.title=''
        parentFolder._setObject(id, self)
        return parentFolder._getOb(id) # as in OSF/Folder.py

    def register_method(self, method):
        self.method = method

    def do_something():
        ...
        value = self.method(start_date, end_date)
        ...

#------------------------- zope error message -------------------------
           Zope Error

           Zope has encountered an error while publishing this resource.

           Error Type:  cPickle.PicklingError
           Error Value: Cannot pickle objects.



           Troubleshooting Suggestions

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                The parameters passed to this resource may be incorrect. 
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                an error. 

           For more detailed information about the error, please refer to
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           If the error persists please contact the site maintainer. Thank
           you for your patience. 




Traceback (innermost last):
  File D:\prog\zope\lib\python\ZPublisher\Publish.py, line 222, in
publish_module
  File D:\prog\zope\lib\python\ZPublisher\Publish.py, line 187, in publish
  File D:\prog\zope\lib\python\Zope\__init__.py, line 221, in
zpublisher_exception_hook
  File D:\prog\zope\lib\python\ZPublisher\Publish.py, line 175, in publish
  File D:\prog\zope\lib\python\Zope\__init__.py, line 235, in commit
  File D:\prog\zope\lib\python\ZODB\Transaction.py, line 252, in commit
  File D:\prog\zope\lib\python\ZODB\Connection.py, line 358, in commit
    (Info: (('Products.HOOP.Calendar', 'Calendar'),
'\000\000\000\000\000\000\024=', ''))

cPickle.PicklingError: (see above)


#------------------------- python shell example -------------------------
>>> class gaga:
...     def nop(self): pass
...     def __init__(self):
...             self.m = self.nop
...     def get(self):
...             return self.m
...
>>> g= gaga()
>>> g
<__main__.gaga instance at 7e8a80>
>>> g.get()
<method gaga.nop of gaga instance at 7e8a80>

_______________________________________________________
Grégoire Weber
Rigistr. 31
CH-8006 Zürich
Switzerland
phone:  +41-(0)1-361 66 11
mobile: +41-(0)79-44 11 457
mailto:gregoire.weber@switzerland.org
Gregi's Handy-Handhabung: http://www.topics.ch/greg/ghh