code: def crossvalidate(self, foldsfile):
          
          options = "-F " + self.format + " " +  self.timbloptions + " -t cross_validate"
          print("Instantiating Timbl API : " + options,file=stderr)
          if sys.version < '3':
              self.api = timblapi.TimblAPI(b(options), b"")
          else:
              self.api = timblapi.TimblAPI(options, "")
          if self.debug:
              print("Enabling debug for timblapi",file=stderr)
              self.api.enableDebug()
          print("Calling Timbl Test : " + options,file=stderr)
          if sys.version < '3':
              self.api.test(b(foldsfile),b'',b'')
          else:
              self.api.test(u(foldsfile),'','')
          a = self.api.getAccuracy()
          del self.api
          return a
docs: Train & Test using cross validation, testfile is a file that contains the filenames of all the folds!