code: def do_prune(self):
          
          if self.prune_table and self.prune_column and self.prune_date:
              return True
          elif self.prune_table or self.prune_column or self.prune_date:
              raise Exception('override zero or all prune variables')
          else:
              return False
docs: Return True if prune_table, prune_column, and prune_date are implemented.
          If only a subset of prune variables are override, an exception is raised to remind the user to implement all or none.
          Prune (data newer than prune_date deleted) before copying new data in.