code: def lookup(self, tokens):
          
          lemmatized_tokens = []
          if type(tokens) == list:
              for token in tokens:
                  # look for token in lemma dict keys
                  if token.lower() in self.lemmata.keys():
                      # `lemmas` is a list of possible lemmata. Probability values must be assigned.
                      # `lemmalist` is a list of the form [(LEMMA, PROBABILITY), (LEMMA, PROBABILITY)]
                      # `lemmaobj` is a tuple with the form (LEMMA, LIST)
                      lemmas = self.lemmata[token.lower()]
                      lemmalist = []
                      for lemma in lemmas:
                          lemmalist.append((lemma, 1/len(lemmas)))
                      lemmaobj = (token, lemmalist)
                  else:
                  # if token not found in lemma-headword list, return the token itself
                      lemmalist = []
                      lemmalist.append((token, 1))
                      lemmaobj = (token, lemmalist)
                  lemmatized_tokens.append(lemmaobj)
          if type(tokens) == str:
              if tokens.lower() in self.lemmata.keys():
                  # `lemmas` is a list of possible lemmata. Probability values must be assigned.
                  # `lemmalist` is a list of the form [(LEMMA, PROBABILITY), (LEMMA, PROBABILITY)]
                  # `lemmaobj` is a tuple with the form (LEMMA, LIST)
                  lemmas = self.lemmata[tokens.lower()]
                  lemmalist = []
                  for lemma in lemmas:
                      lemmalist.append((lemma, 1/len(lemmas)))
                  lemmaobj = (tokens, lemmalist)
              else:
              # if token not found in lemma-headword list, return the token itself
                  lemmalist = []
                  lemmalist.append((tokens, 1))
                  lemmaobj = (tokens, lemmalist)
              lemmatized_tokens.append(lemmaobj)
          return lemmatized_tokens
docs: Return a list of possible lemmata and their probabilities for each token