code: def filter_for_pos(self, required_pos, simplify_pos=True):
          
          if type(required_pos) not in (tuple, list, set) \
                  and required_pos is not None \
                  and not isinstance(required_pos, str):
              raise ValueError('`required_pos` must be a string, tuple, list, set or None')
  
          self._require_pos_tags()
  
          self._invalidate_workers_tokens()
  
          logger.info('filtering tokens for POS tag `%s`' % required_pos)
          self._send_task_to_workers('filter_for_pos',
                                     required_pos=required_pos,
                                     pos_tagset=self.pos_tagset,
                                     simplify_pos=simplify_pos)
  
          return self
docs: Filter tokens for a specific POS tag (if `required_pos` is a string) or several POS tags (if `required_pos`
          is a list/tuple/set of strings). The POS tag depends on the tagset used during tagging. If `simplify_pos` is
          True, then the tags are matched to the following simplified forms:
          - 'N' for nouns
          - 'V' for verbs
          - 'ADJ' for adjectives
          - 'ADV' for adverbs
          - None for all other