[Zope] total size of files in a folder

Hi, I want to get the total size of a folder. I do a loop over all files in the folder, but it gives me only the size of the last file in the folder: <dtml-let total_size="0"> <dtml-in "Files.objectValues()"> #Files is the name of my folder <dtml-let total_size="total_size+size"> <dtml-if sequence-end> <dtml-var total_size> </dtml-if> </dtml-let> </dtml-in> </dtml-let> Alternatively, is there simply a variable I can lookup to get the size of the folder? Thank you, Marcus