[Zope] Truncating strings with DTML

Hi All, I'd like to take a string like: /Computers/Data_Formats/Almost_Every_File_Format_in_the_World and cut it down to: /Computers/Data_Formats using DTML. I've tried to count to the last "/", and then truncate the string with ljust, like so: <dtml-let strDirPathSize="_.string.rfind(strDirPath, '/')"> <dtml-let strDirPath="_.string.ljust(strDirPath, strDirPathSize)"> However, ljust/rjust won't truncate the string. In the case above, I know that I want to truncate the string to 23 characters (/Computers/Data_Formats). Is there a way to accomplish this in DTML? If not, any suggestions? Thanks in advance, Aaron