code: def _set_preprocess(sets, **kwargs):
      
      axis            = kwargs.get('axis', semantics.axis_default)
      assume_unique   = kwargs.get('assume_unique', False)
  
      if assume_unique:
          sets = [as_index(s, axis=axis).unique for s in sets]
      else:
          sets = [as_index(s, axis=axis).unique for s in sets]
      return sets
docs: upcasts a sequence of indexable objects to Index objets according to the given kwargs
  
      Parameters
      ----------
      sets : iterable of indexable objects
      axis : int, optional
          axis to view as item sequence
      assume_unique : bool, optional
          if we should assume the items sequence does not contain duplicates
  
      Returns
      -------
      list of Index objects
  
      Notes
      -----
      common preprocessing for all set operations