code: def jaccard_merge(brands, exemplars):
      
      scores = {}
      exemplar_followers = set()
      for followers in exemplars.values():
          exemplar_followers |= followers
  
      for brand, followers in brands:
          scores[brand] = _jaccard(followers, exemplar_followers)
      return scores
docs: Return the average Jaccard similarity between a brand's followers and
      the followers of each exemplar. We merge all exemplar followers into one
      big pseudo-account.