def _get_pairs(self, word):
            """Return set of symbol pairs in a word.
            Word is represented as tuple of symbols (symbols being variable-length strings).
            """
            pairs = set()
            prev_char = word[0]
            for char in word[1:]:
                pairs.add((prev_char, char))
                prev_char = char
            return pairs
Return set of symbol pairs in a word.
            Word is represented as tuple of symbols (symbols being variable-length strings).
            
ptstructure/vqa/pytorchnlp/transformers/tokenizer_utils.py