[Zope] calling python from template

I want to call a python script from a page template but I don't know how to 'name' the script, ie I don't know how acquisition will find it. my script lives if /folderA/folderB by page templated list is /folderA/folderB/folderC I use <p tal:content="python:listObjects('departments', 'priority')">content of listObjects </p> to call the listObjects script in folderB -- but zope isn't finding it. what simple thing am I missing?