thank you! may be some pseudocode would help.
defaultdict(<function torchtext.vocab._default_unk_index>,
            {'#': 40,
             '$': 21,
             "''": 26,
             '(': 35,
             ')': 34,
             ',': 8,
             '.': 11,
             ':': 27,
             '<pad>': 1,
             '<unk>': 0, # that's it! th <unk>
             'CC': 13,
             'CD': 9,
             'DT': 5,
             'EX': 37,
             'FW': 43,
             'IN': 4,
             'JJ': 7,
             'JJR': 29,
             'JJS': 32,
             'LS': 41,
             'MD': 23,
             'NN': 2,
             'NNP': 3,
             'NNPS': 44,
             'NNS': 6,
             'PDT': 45,
             'POS': 20,
             'PRP': 19,
             'PRP$': 24,
             'RB': 12,
             'RBR': 31,
             'RBS': 38,
             'RP': 30,
             'TO': 15,
             'UH': 42,
             'VB': 14,
             'VBD': 10,
             'VBG': 18,
             'VBN': 16,
             'VBP': 22,
             'VBZ': 17,
             'WDT': 28,
             'WP': 33,
             'WP$': 39,
             'WRB': 36,
             '``': 25})

May be a non-sequential Field would help. I would try to figure that out.