hi, i'm very new to zope and am trying to get familiar with the variety of mechanisms i can use. zope is indeed a very nice package! i am starting with version 2.3.0a1 (because it matches the book). i've not yet had success getting preconditions to work with file objects. i hope i'm not doing anything too bone-headed. here is what i have: in a folder i have file objects T and U. T has the precondition 'preco(1)' and U has the precondition 'preco(0)'. in the same folder (or above, it doesn't matter) i have the python script preco with the contents if r == 0: raise "preco" else: return r when i the manager or type in the URL directly i can view/download both T and U. i was hoping only T would be "visible". i'm not sure how to debug something like this. if you can tell me how i can debug this on my own that would be best. -cheers