[Zope] How to check with ZOPE/Python if file "x.html" exists in path container.REQUEST.PARENTS[0].getPhysicalPath()?

I simply want to check in a ZOPE/Python script, whether the file "x.html" exists at the exact path defined by container.REQUEST.PARENTS[0].getPhysicalPath(). And I want to make sure that ZOPE does NO TRAVERSAL, i.e. does not look in folders above the given path in case the file was not found. The statement path = container.REQUEST.PARENTS[0].getPhysicalPath() returns correctly something like: path = "('', 'silva', 'kom', 'web', 'topic1', 'subtopic1a')" The Python script "checkFile.py" to check for the file will reside at /silva/kom/checkFile.py and is called from a tal:define="fileExists python:here.checkFile('x.html'))" in /silva/kom/web/main.html. Any idea how I can do that? Thanks for your answers. Regards, Thomas