Initialize token information from a list of subtoken strings.

def _init_subtokens_from_list(self, subtoken_strings):
        """Initialize token information from a list of subtoken strings."""
        # we remember the maximum length of any subtoken to avoid having to
        # check arbitrarily long strings.
        self._all_subtoken_strings = set([s for s in subtoken_strings if s])
        self._max_subtoken_len = max([len(s) for s in subtoken_strings])