Initializes the encoder from a list of subwords.

def _init_from_list(self, subwords):
    """Initializes the encoder from a list of subwords."""
    subwords = [tf.compat.as_text(s) for s in subwords if s]
    self._subwords = subwords
    # Note that internally everything is 0-indexed. Padding is dealt with at the
    # end of encode and the beginning of decode.
    self._subword_to_id = {s: i for i, s in enumerate(subwords)}

    # We remember the maximum length of any subword to avoid having to
    # check arbitrarily long strings.
    self._max_subword_len = max(
        len(_UNDERSCORE_REPLACEMENT), max([len(s) for s in subwords] or [1]))

    # Initialize the cache
    self._cache_size = 2**20
    self._token_to_ids_cache = [(None, None)] * self._cache_size

    # Setup tokenizer
    # Reserved tokens are all tokens that are mixed alphanum and non-alphanum.
    reserved_tokens = set([_UNDERSCORE_REPLACEMENT])
    for t in self._subwords:
      if text_encoder.is_mixed_alphanum(t):
        reserved_tokens.add(t)
    self._tokenizer = text_encoder.Tokenizer(
        alphanum_only=False, reserved_tokens=reserved_tokens)