class_docstr: Filter examples by class label.
  
  --mutators <this_mutator>
class_docstr_tok: ["Filter","examples","by","class","label",".","--","mutators","<","this_mutator",">"]
code: def many_episode_mutation(self, episode):
      out_episodes = []
      for message in episode:
          if self.target_class in message["labels"]:
              out_episodes.append([message])
      return out_episodes
  
imports: from string import punctuation
  import copy
  from typing import List
  from parlai.core.mutators import register_mutator, ManyEpisodeMutator, MessageMutator
  from parlai.core.message import Message
  from parlai.mutators.flatten import FlattenMutator
  from parlai.utils.strings import normalize_reply
  from parlai.tasks.wizard_of_wikipedia.agents import TOKEN_KNOWLEDGE, TOKEN_END_KNOWLEDGE
  from parlai.tasks.wizard_of_internet import constants
  from .constants import FeedbackType, UNWANTED_TOKENS
label_desc: Use image node_id 1 for calling the SingleClassMixin obj's underlying member method code with example usage: obj.many_episode_mutation(episode) and returns: out_episodes