[Zope] Retrieve calling object from python script

[Robin Breathe]

I've written a cache parameter script in Python, which is designed to be 
called without arguments from a dtml page, zpt or as a precondition to a 
File or Image object. It needs to get a handle on the item which called 
it (I'll call that handle 'object'), to retrieve optional script 
parameters stored as properties of the calling object. This allows per 
instance configuration of ZPTs, and suchlike.

Here's the start of the script:

#start
request  = context.REQUEST
object   = request.PUBLISHED
response = request.RESPONSE

# DEBUG: look at PUBLISHED
response.setHeader('Published-Object', repr(object))

try:
     object.getId()
except:
     object = context

# function shortcuts
hasProperty = object.propertysheets.hasProperty
getProperty = object.propertysheets.getProperty
#...
#end

So, for ZPTs I call the script with 'here/cache', and I get:

     Published-Object: <ZopePageTemplate at index_html>

...'context' alone gives a handle on the item's container (e.g. Folder). 
This is fine.

Now, for Files and Images, a set the Precondition to 'cache' and I get:

     Published-Object: <bound method File.index_html of <File instance 
at a045230>>

...the .getId() fails, and it uses context, which works (e.g. I can 
access the File's propertysheets), but isn't beautiful.

However, this fails for ZCGI objects. I get:

Published-Object: <bound method ZCGIFolder.index_html of <ZCGIFolder at 
/Base/ht-bin>>

...but 'context' refers to the <CMFSite instance>, /Base, not to the 
ZCGIFolder, /Base/ht-bin.

So the question is this: what's the proper way to identify the object 
whose method has been bound to REQUEST.PUBLISHED, or if that's the wrong 
route, to simply, reliably identify the caller of a python script which 
can be called from a range of different object types?

Thanks,
- Robin
-- 
Robin Breathe, Computer Services, Oxford Brookes University, Oxford, UK
rbreathe at brookes.ac.uk       Tel: +44 1865 483323  Fax: +44 1865 483073