code: def combine_duplicates(self):
          
          if self.unique_stmts is None:
              self.unique_stmts = self.combine_duplicate_stmts(self.stmts)
          return self.unique_stmts
docs: Combine duplicates among `stmts` and save result in `unique_stmts`.
  
          A wrapper around the static method :py:meth:`combine_duplicate_stmts`.