code: def _checkpoint_out_filenames(self):
          
          out_filenames = []
          if self.Parameters['-n'].isOn():
              out_name = str(self.Parameters['-n'].Value)
              walk_root = self.WorkingDir
              if self.Parameters['-w'].isOn():
                  walk_root = str(self.Parameters['-w'].Value)
              for tup in walk(walk_root):
                  dpath, dnames, dfiles = tup
                  if dpath == walk_root:
                      for gen_file in dfiles:
                          if out_name in gen_file and "checkpoint" in gen_file:
                              out_filenames.append(walk_root + gen_file)
                      break
  
          else:
              raise ValueError, "No output file specified."
          return out_filenames
docs: RAxML generates a crapload of checkpoint files so need to
          walk directory to collect names of all of them.