code: def _build_vocab(self, sentences, markers=[]):
          
          from snorkel.learning.pytorch.rnn.utils import SymbolTable
  
          vocab = Counter()
          for sent in sentences:
              for w in sent:
                  vocab[w] += 1
          word_dict = SymbolTable()
          list(map(word_dict.get, vocab))
          list(map(word_dict.get, markers))
          return word_dict
docs: Initalize symbol table dictionary
  
          :param sentences:
          :param markers:
          :return: