code: def pick_inputs(workspace):
      
      frags_present = set()
      frags_absent = set()
  
      for path in workspace.input_paths:
          if workspace.fragments_missing(path):
              frags_absent.add(path)
          else:
              frags_present.add(path)
  
      # If no fragments have been generated yet, just return the directory to 
      # make the resulting 'klab_generate_fragments' command a little simpler.
      if not frags_present:
          return [workspace.input_dir]
  
      print '{0} of {1} inputs are missing fragments.'.format(
          len(frags_absent), len(workspace.input_paths))
  
      return sorted(frags_absent)
docs: Figure out which inputs don't yet have fragments.
      
      This is useful when some of your fragment generation jobs fail and you need 
      to rerun them.