tokenization_utils.py

# coding=utf-8
# Copyright 2020 The HuggingFace Inc. team.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
 Tokenization classes for python tokenizers. For fast tokenizers (provided by HuggingFace's tokenizers library) see
 tokenization_utils_fast.py
"""
import bisect
import itertools
import re
import unicodedata
from collections import OrderedDict
from typing import Any, Dict, List, Optional, Tuple, Union, overload

from .tokenization_utils_base import (
    ENCODE_KWARGS_DOCSTRING,
    ENCODE_PLUS_ADDITIONAL_KWARGS_DOCSTRING,
    INIT_TOKENIZER_DOCSTRING,
    AddedToken,
    BatchEncoding,
    EncodedInput,
    EncodedInputPair,
    PreTokenizedInput,
    PreTokenizedInputPair,
    PreTrainedTokenizerBase,
    TextInput,
    TextInputPair,
    TruncationStrategy,
)
from .utils import PaddingStrategy, TensorType, add_end_docstrings, logging


logger = logging.get_logger(__name__)

# Slow tokenizers are saved in a vocabulary plus three separated files
SPECIAL_TOKENS_MAP_FILE = "special_tokens_map.json"
ADDED_TOKENS_FILE = "added_tokens.json"
TOKENIZER_CONFIG_FILE = "tokenizer_config.json"


class Trie:
    """
    Trie in Python. Creates a Trie out of a list of words. The trie is used to split on `added_tokens` in one pass
    Loose reference https://en.wikipedia.org/wiki/Trie
    """

    def __init__(self):
        self.data = {}

    def add(self, word: str):
        """
        Passes over every char (utf-8 char) on word and recursively adds it to the internal `data` trie representation.
        The special key `""` is used to represent termination.

        This function is idempotent, adding twice the same word will leave the trie unchanged

        Example:

        ```python
        >>> trie = Trie()
        >>> trie.add("Hello 友達")
        >>> trie.data
        {"H": {"e": {"l": {"l": {"o": {" ": {"友": {"達": {"": 1}}}}}}}}}

        >>> trie.add("Hello")
        >>> trie.data
        {"H": {"e": {"l": {"l": {"o": {"": 1, " ": {"友": {"達": {"": 1}}}}}}}}}
        ```
        """
        if not word:
            # Prevent empty string
            return
        ref = self.data
        for char in word:
            ref[char] = char in ref and ref[char] or {}
            ref = ref[char]
        ref[""] = 1

    def split(self, text: str) -> List[str]:
        """
        Will look for the words added to the trie within `text`. Output is the original string splitted along the
        boundaries of the words found.

        This trie will match the longest possible word first !

        Example:

        ```python
        >>> trie = Trie()
        >>> trie.split("[CLS] This is a extra_id_100")
        ["[CLS] This is a extra_id_100"]

        >>> trie.add("[CLS]")
        >>> trie.add("extra_id_1")
        >>> trie.add("extra_id_100")
        >>> trie.split("[CLS] This is a extra_id_100")
        ["[CLS]", " This is a ", "extra_id_100"]
        ```
        """
        # indexes are counted left of the chars index.
        # "hello", index 0, is left of h, index 1 is between h and e.
        # index 5 is right of the "o".

        # States are going to capture every possible start (indexes as above)
        # as keys, and have as values, a pointer to the position in the trie
        # where we're at. This is a partial match for now.
        # This enables to keep track of multiple matches while we're iterating
        # the string
        # If the trie contains, "blowing", and "lower" and we encounter the
        # string "blower", we need to split into ["b", "lower"].
        # This is where we need to keep track of multiple possible starts.
        states = OrderedDict()

        # This will contain every indices where we need
        # to cut.
        # We force to cut at offset 0 and len(text) (added later)
        offsets = [0]

        # This is used by the lookahead which needs to skip over
        # some text where the full match exceeded the place in the initial
        # for loop
        skip = 0
        # Main loop, Giving this algorithm O(n) complexity
        for current, current_char in enumerate(text):
            if skip and current < skip:
                # Prevents the lookahead for matching twice
                # like extra_id_100 and id_100
                continue

            # This will track every state
            # that stop matching, we need to stop tracking them.
            # If we look at "lowball", we're going to match "l" (add it to states), "o", "w", then
            # fail on "b", we need to remove 0 from the valid states.
            to_remove = set()
            # Whenever we found a match, we need to drop everything
            # this is a greedy algorithm, it will match on the first found token
            reset = False

            # In this case, we already have partial matches (But unfinished)
            for start, trie_pointer in states.items():
                if "" in trie_pointer:
                    # This is a final match, we need to reset and
                    # store the results in `offsets`.

                    # Lookahead to match longest first
                    # Important in case of extra_id_1 vs extra_id_100
                    # Here we are also actively looking for other earlier partial
                    # matches
                    # "[CLS]", "L", we need to match CLS even if L is special
                    for lookstart, looktrie_pointer in states.items():
                        if lookstart > start:
                            # This partial match is later, we can stop looking
                            break
                        elif lookstart < start:
                            # This partial match is earlier, the trie pointer
                            # was already updated, so index is + 1
                            lookahead_index = current + 1
                            end = current + 1
                        else:
                            # Here lookstart == start and
                            #      looktrie_pointer == trie_pointer
                            # It wasn't updated yet so indices are current ones
                            lookahead_index = current
                            end = current
                        next_char = text[lookahead_index] if lookahead_index < len(text) else None
                        if "" in looktrie_pointer:
                            start = lookstart
                            end = lookahead_index
                            skip = lookahead_index

                        while next_char in looktrie_pointer:
                            looktrie_pointer = looktrie_pointer[next_char]
                            lookahead_index += 1
                            if "" in looktrie_pointer:
                                start = lookstart
                                end = lookahead_index
                                skip = lookahead_index

                            if lookahead_index == len(text):
                                # End of string
                                break
                            next_char = text[lookahead_index]
                        # End lookahead

                    # Storing and resetting
                    offsets.append(start)
                    offsets.append(end)
                    reset = True
                    break
                elif current_char in trie_pointer:
                    # The current character being looked at has a match within the trie
                    # update the pointer (it will be stored back into states later).
                    trie_pointer = trie_pointer[current_char]

                    # Storing back the new pointer into the states.
                    # Partial matches got longer by one.
                    states[start] = trie_pointer
                else:
                    # The new character has not match in the trie, we need
                    # to stop keeping track of this partial match.
                    # We can't do it directly within the loop because of how
                    # python iteration works
                    to_remove.add(start)

            # Either clearing the full start (we found a real match)
            # Or clearing only the partial matches that didn't work.
            if reset:
                states = {}
            else:
                for start in to_remove:
                    del states[start]

            # If this character is a starting character within the trie
            # start keeping track of this partial match.
            if current >= skip and current_char in self.data:
                states[current] = self.data[current_char]

        # We have a cut at the end with states.
        for start, trie_pointer in states.items():
            if "" in trie_pointer:
                # This is a final match, we need to reset and
                # store the results in `offsets`.
                end = len(text)
                offsets.append(start)
                offsets.append(end)
                # Longest cut is always the one with lower start so the first
                # item so we need to break.
                break

        return self.cut_text(text, offsets)

    def cut_text(self, text, offsets):
        # We have all the offsets now, we just need to do the actual splitting.
        # We need to eventually add the first part of the string and the eventual
        # last part.
        offsets.append(len(text))
        tokens = []
        start = 0
        for end in offsets:
            if start > end:
                logger.error(
                    "There was a bug in Trie algorithm in tokenization. Attempting to recover. Please report it"
                    " anyway."
                )
                continue
            elif start == end:
                # This might happen if there's a match at index 0
                # we're also preventing zero-width cuts in case of two
                # consecutive matches
                continue
            tokens.append(text[start:end])
            start = end

        return tokens


def _is_whitespace(char):
    """Checks whether `char` is a whitespace character."""
    # \t, \n, and \r are technically control characters but we treat them
    # as whitespace since they are generally considered as such.
    if char == " " or char == "\t" or char == "\n" or char == "\r":
        return True
    cat = unicodedata.category(char)
    if cat == "Zs":
        return True
    return False


def _is_control(char):
    """Checks whether `char` is a control character."""
    # These are technically control characters but we count them as whitespace
    # characters.
    if char == "\t" or char == "\n" or char == "\r":
        return False
    cat = unicodedata.category(char)
    if cat.startswith("C"):
        return True
    return False


def _is_punctuation(char):
    """Checks whether `char` is a punctuation character."""
    cp = ord(char)
    # We treat all non-letter/number ASCII as punctuation.
    # Characters such as "^", "$", and "`" are not in the Unicode
    # Punctuation class but we treat them as punctuation anyways, for
    # consistency.
    if (cp >= 33 and cp <= 47) or (cp >= 58 and cp <= 64) or (cp >= 91 and cp <= 96) or (cp >= 123 and cp <= 126):
        return True
    cat = unicodedata.category(char)
    if cat.startswith("P"):
        return True
    return False


def _is_end_of_word(text):
    """Checks whether the last character in text is one of a punctuation, control or whitespace character."""
    last_char = text[-1]
    return bool(_is_control(last_char) | _is_punctuation(last_char) | _is_whitespace(last_char))


def _is_start_of_word(text):
    """Checks whether the first character in text is one of a punctuation, control or whitespace character."""
    first_char = text[0]
    return bool(_is_control(first_char) | _is_punctuation(first_char) | _is_whitespace(first_char))


def _insert_one_token_to_ordered_list(token_list: List[str], new_token: str):
    """
    Inserts one token to an ordered list if it does not already exist. Note: token_list must be sorted.
    """
    insertion_idx = bisect.bisect_left(token_list, new_token)
    # Checks if new_token is already in the ordered token_list
    if insertion_idx < len(token_list) and token_list[insertion_idx] == new_token:
        # new_token is in token_list, don't add
        return
    else:
        token_list.insert(insertion_idx, new_token)


@add_end_docstrings(INIT_TOKENIZER_DOCSTRING)
class PreTrainedTokenizer(PreTrainedTokenizerBase):
    """
    Base class for all slow tokenizers.

    Inherits from [`~tokenization_utils_base.PreTrainedTokenizerBase`].

    Handle all the shared methods for tokenization and special tokens as well as methods downloading/caching/loading
    pretrained tokenizers as well as adding tokens to the vocabulary.

    This class also contain the added tokens in a unified way on top of all tokenizers so we don't have to handle the
    specific vocabulary augmentation methods of the various underlying dictionary structures (BPE, sentencepiece...).
    """

    def __init__(self, **kwargs):
        super().__init__(**kwargs)

        # Added tokens - We store this for both slow and fast tokenizers
        # until the serialization of Fast tokenizers is updated
        self.added_tokens_encoder: Dict[str, int] = {}
        self.added_tokens_decoder: Dict[int, str] = {}
        self.unique_no_split_tokens: List[str] = []
        self.tokens_trie = Trie()

        self._decode_use_source_tokenizer = False

    @property
    def is_fast(self) -> bool:
        return False

    @property
    def vocab_size(self) -> int:
        """
        `int`: Size of the base vocabulary (without the added tokens).
        """
        raise NotImplementedError

    def get_added_vocab(self) -> Dict[str, int]:
        """
        Returns the added tokens in the vocabulary as a dictionary of token to index.

        Returns:
            `Dict[str, int]`: The added tokens.
        """
        return self.added_tokens_encoder

    def __len__(self):
        """
        Size of the full vocabulary with the added tokens.
        """
        return self.vocab_size + len(self.added_tokens_encoder)

    def _add_tokens(self, new_tokens: Union[List[str], List[AddedToken]], special_tokens: bool = False) -> int:
        """
        Add a list of new tokens to the tokenizer class. If the new tokens are not in the vocabulary, they are added to
        it with indices starting from length of the current vocabulary.

        Args:
            new_tokens (`List[str]`or `List[tokenizers.AddedToken]`):
                Token(s) to add in vocabulary. A token is only added if it's not already in the vocabulary (tested by
                checking if the tokenizer assign the index of the `unk_token` to them).
            special_tokens (`bool`, *optional*, defaults to `False`):
                Whether or not the tokens should be added as special tokens.

        Returns:
            `int`: The number of tokens actually added to the vocabulary.

        Examples:

        ```python
        # Let's see how to increase the vocabulary of Bert model and tokenizer
        tokenizer = BertTokenizer.from_pretrained("bert-base-uncased")
        model = BertModel.from_pretrained("bert-base-uncased")

        num_added_toks = tokenizer.add_tokens(["new_tok1", "my_new-tok2"])
        print("We have added", num_added_toks, "tokens")
        # Note: resize_token_embeddings expects to receive the full size of the new vocabulary, i.e. the length of the tokenizer.
        model.resize_token_embeddings(len(tokenizer))
        ```"""
        new_tokens = [str(tok) for tok in new_tokens]

        tokens_to_add = []
        for token in new_tokens:
            if not isinstance(token, str):
                raise TypeError(f"Token {token} is not a string but a {type(token)}.")
            if not special_tokens and hasattr(self, "do_lower_case") and self.do_lower_case:
                token = token.lower()
            if (
                token != self.unk_token
                and self.convert_tokens_to_ids(token) == self.convert_tokens_to_ids(self.unk_token)
                and token not in tokens_to_add
            ):
                tokens_to_add.append(token)
                if self.verbose:
                    logger.info(f"Adding {token} to the vocabulary")

        added_tok_encoder = {tok: len(self) + i for i, tok in enumerate(tokens_to_add)}
        added_tok_decoder = {v: k for k, v in added_tok_encoder.items()}
        self.added_tokens_encoder.update(added_tok_encoder)
        self.added_tokens_decoder.update(added_tok_decoder)

        # Make sure we don't split on any special tokens (even they were already in the vocab before e.g. for Albert)
        if special_tokens:
            if len(new_tokens) == 1:
                _insert_one_token_to_ordered_list(self.unique_no_split_tokens, new_tokens[0])
            else:
                self.unique_no_split_tokens = sorted(set(self.unique_no_split_tokens).union(set(new_tokens)))
        else:
            # Or on the newly added tokens
            if len(tokens_to_add) == 1:
                _insert_one_token_to_ordered_list(self.unique_no_split_tokens, tokens_to_add[0])
            else:
                self.unique_no_split_tokens = sorted(set(self.unique_no_split_tokens).union(set(tokens_to_add)))
        self._create_trie(self.unique_no_split_tokens)

        return len(tokens_to_add)

    def _create_trie(self, unique_no_split_tokens):
        trie = Trie()
        for token in unique_no_split_tokens:
            if hasattr(self, "do_lower_case") and self.do_lower_case and token not in self.all_special_tokens:
                trie.add(token.lower())
            else:
                trie.add(token)
        self.tokens_trie = trie

    def num_special_tokens_to_add(self, pair: bool = False) -> int:
        """
        Returns the number of added tokens when encoding a sequence with special tokens.

        <Tip>

        This encodes a dummy input and checks the number of added tokens, and is therefore not efficient. Do not put
        this inside your training loop.

        </Tip>

        Args:
            pair (`bool`, *optional*, defaults to `False`):
                Whether the number of added tokens should be computed in the case of a sequence pair or a single
                sequence.

        Returns:
            `int`: Number of special tokens added to sequences.
        """
        token_ids_0 = []
        token_ids_1 = []
        return len(self.build_inputs_with_special_tokens(token_ids_0, token_ids_1 if pair else None))

    def tokenize(self, text: TextInput, **kwargs) -> List[str]:
        """
        Converts a string in a sequence of tokens, using the tokenizer.

        Split in words for word-based vocabulary or sub-words for sub-word-based vocabularies
        (BPE/SentencePieces/WordPieces). Takes care of added tokens.

        Args:
            text (`str`):
                The sequence to be encoded.
            **kwargs (additional keyword arguments):
                Passed along to the model-specific `prepare_for_tokenization` preprocessing method.

        Returns:
            `List[str]`: The list of tokens.
        """
        # Simple mapping string => AddedToken for special tokens with specific tokenization behaviors
        all_special_tokens_extended = {
            str(t): t for t in self.all_special_tokens_extended if isinstance(t, AddedToken)
        }

        text, kwargs = self.prepare_for_tokenization(text, **kwargs)

        if kwargs:
            logger.warning(f"Keyword arguments {kwargs} not recognized.")

        # TODO: should this be in the base class?
        if hasattr(self, "do_lower_case") and self.do_lower_case:
            # convert non-special tokens to lowercase
            escaped_special_toks = [
                re.escape(s_tok) for s_tok in (self.unique_no_split_tokens + self.all_special_tokens)
            ]
            pattern = r"(" + r"|".join(escaped_special_toks) + r")|" + r"(.+?)"
            text = re.sub(pattern, lambda m: m.groups()[0] or m.groups()[1].lower(), text)

        no_split_token = set(self.unique_no_split_tokens)
        tokens = self.tokens_trie.split(text)
        # ["This is something", "<special_token_1>", "  else"]
        for i, token in enumerate(tokens):
            if token in no_split_token:
                tok_extended = all_special_tokens_extended.get(token, None)
                left = tokens[i - 1] if i > 0 else None
                right = tokens[i + 1] if i < len(tokens) - 1 else None
                if isinstance(tok_extended, AddedToken):
                    if tok_extended.rstrip and right:
                        # A bit counter-intuitive but we strip the left of the string
                        # since tok_extended.rstrip means the special token is eating all white spaces on its right
                        tokens[i + 1] = right.lstrip()
                    # Strip white spaces on the left
                    if tok_extended.lstrip and left:
                        tokens[i - 1] = left.rstrip()  # Opposite here
                else:
                    # We strip left and right by default
                    if right:
                        tokens[i + 1] = right.lstrip()
                    if left:
                        tokens[i - 1] = left.rstrip()
        # ["This is something", "<special_token_1>", "else"]
        tokenized_text = []
        for token in tokens:
            # Need to skip eventual empty (fully stripped) tokens
            if not token:
                continue
            if token in no_split_token:
                tokenized_text.append(token)
            else:
                tokenized_text.extend(self._tokenize(token))
        # ["This", " is", " something", "<special_token_1>", "else"]
        return tokenized_text

    def _tokenize(self, text, **kwargs):
        """
        Converts a string in a sequence of tokens (string), using the tokenizer. Split in words for word-based
        vocabulary or sub-words for sub-word-based vocabularies (BPE/SentencePieces/WordPieces).

        Do NOT take care of added tokens.
        """
        raise NotImplementedError

    def convert_tokens_to_ids(self, tokens: Union[str, List[str]]) -> Union[int, List[int]]:
        """
        Converts a token string (or a sequence of tokens) in a single integer id (or a sequence of ids), using the
        vocabulary.

        Args:
            tokens (`str` or `List[str]`): One or several token(s) to convert to token id(s).

        Returns:
            `int` or `List[int]`: The token id or list of token ids.
        """
        if tokens is None:
            return None

        if isinstance(tokens, str):
            return self._convert_token_to_id_with_added_voc(tokens)

        ids = []
        for token in tokens:
            ids.append(self._convert_token_to_id_with_added_voc(token))
        return ids

    def _convert_token_to_id_with_added_voc(self, token):
        if token is None:
            return None

        if token in self.added_tokens_encoder:
            return self.added_tokens_encoder[token]
        return self._convert_token_to_id(token)

    def _convert_token_to_id(self, token):
        raise NotImplementedError

    def _encode_plus(
        self,
        text: Union[TextInput, PreTokenizedInput, EncodedInput],
        text_pair: Optional[Union[TextInput, PreTokenizedInput, EncodedInput]] = None,
        add_special_tokens: bool = True,
        padding_strategy: PaddingStrategy = PaddingStrategy.DO_NOT_PAD,
        truncation_strategy: TruncationStrategy = TruncationStrategy.DO_NOT_TRUNCATE,
        max_length: Optional[int] = None,
        stride: int = 0,
        is_split_into_words: bool = False,
        pad_to_multiple_of: Optional[int] = None,
        return_tensors: Optional[Union[str, TensorType]] = None,
        return_token_type_ids: Optional[bool] = None,
        return_attention_mask: Optional[bool] = None,
        return_overflowing_tokens: bool = False,
        return_special_tokens_mask: bool = False,
        return_offsets_mapping: bool = False,
        return_length: bool = False,
        verbose: bool = True,
        **kwargs,
    ) -> BatchEncoding:
        def get_input_ids(text):
            if isinstance(text, str):
                tokens = self.tokenize(text, **kwargs)
                return self.convert_tokens_to_ids(tokens)
            elif isinstance(text, (list, tuple)) and len(text) > 0 and isinstance(text[0], str):
                if is_split_into_words:
                    tokens = list(
                        itertools.chain(*(self.tokenize(t, is_split_into_words=True, **kwargs) for t in text))
                    )
                    return self.convert_tokens_to_ids(tokens)
                else:
                    return self.convert_tokens_to_ids(text)
            elif isinstance(text, (list, tuple)) and len(text) > 0 and isinstance(text[0], int):
                return text
            else:
                if is_split_into_words:
                    raise ValueError(
                        f"Input {text} is not valid. Should be a string or a list/tuple of strings when"
                        " `is_split_into_words=True`."
                    )
                else:
                    raise ValueError(
                        f"Input {text} is not valid. Should be a string, a list/tuple of strings or a list/tuple of"
                        " integers."
                    )

        if return_offsets_mapping:
            raise NotImplementedError(
                "return_offset_mapping is not available when using Python tokenizers. "
                "To use this feature, change your tokenizer to one deriving from "
                "transformers.PreTrainedTokenizerFast. "
                "More information on available tokenizers at "
                "https://github.com/huggingface/transformers/pull/2674"
            )

        first_ids = get_input_ids(text)
        second_ids = get_input_ids(text_pair) if text_pair is not None else None

        return self.prepare_for_model(
            first_ids,
            pair_ids=second_ids,
            add_special_tokens=add_special_tokens,
            padding=padding_strategy.value,
            truncation=truncation_strategy.value,
            max_length=max_length,
            stride=stride,
            pad_to_multiple_of=pad_to_multiple_of,
            return_tensors=return_tensors,
            prepend_batch_axis=True,
            return_attention_mask=return_attention_mask,
            return_token_type_ids=return_token_type_ids,
            return_overflowing_tokens=return_overflowing_tokens,
            return_special_tokens_mask=return_special_tokens_mask,
            return_length=return_length,
            verbose=verbose,
        )

    def _batch_encode_plus(
        self,
        batch_text_or_text_pairs: Union[
            List[TextInput],
            List[TextInputPair],
            List[PreTokenizedInput],
            List[PreTokenizedInputPair],
            List[EncodedInput],
            List[EncodedInputPair],
        ],
        add_special_tokens: bool = True,
        padding_strategy: PaddingStrategy = PaddingStrategy.DO_NOT_PAD,
        truncation_strategy: TruncationStrategy = TruncationStrategy.DO_NOT_TRUNCATE,
        max_length: Optional[int] = None,
        stride: int = 0,
        is_split_into_words: bool = False,
        pad_to_multiple_of: Optional[int] = None,
        return_tensors: Optional[Union[str, TensorType]] = None,
        return_token_type_ids: Optional[bool] = None,
        return_attention_mask: Optional[bool] = None,
        return_overflowing_tokens: bool = False,
        return_special_tokens_mask: bool = False,
        return_offsets_mapping: bool = False,
        return_length: bool = False,
        verbose: bool = True,
        **kwargs,
    ) -> BatchEncoding:
        def get_input_ids(text):
            if isinstance(text, str):
                tokens = self.tokenize(text, **kwargs)
                return self.convert_tokens_to_ids(tokens)
            elif isinstance(text, (list, tuple)) and len(text) > 0 and isinstance(text[0], str):
                if is_split_into_words:
                    tokens = list(
                        itertools.chain(*(self.tokenize(t, is_split_into_words=True, **kwargs) for t in text))
                    )
                    return self.convert_tokens_to_ids(tokens)
                else:
                    return self.convert_tokens_to_ids(text)
            elif isinstance(text, (list, tuple)) and len(text) > 0 and isinstance(text[0], int):
                return text
            else:
                raise ValueError(
                    "Input is not valid. Should be a string, a list/tuple of strings or a list/tuple of integers."
                )

        if return_offsets_mapping:
            raise NotImplementedError(
                "return_offset_mapping is not available when using Python tokenizers. "
                "To use this feature, change your tokenizer to one deriving from "
                "transformers.PreTrainedTokenizerFast."
            )

        input_ids = []
        for ids_or_pair_ids in batch_text_or_text_pairs:
            if not isinstance(ids_or_pair_ids, (list, tuple)):
                ids, pair_ids = ids_or_pair_ids, None
            elif is_split_into_words and not isinstance(ids_or_pair_ids[0], (list, tuple)):
                ids, pair_ids = ids_or_pair_ids, None
            else:
                ids, pair_ids = ids_or_pair_ids

            first_ids = get_input_ids(ids)
            second_ids = get_input_ids(pair_ids) if pair_ids is not None else None
            input_ids.append((first_ids, second_ids))

        batch_outputs = self._batch_prepare_for_model(
            input_ids,
            add_special_tokens=add_special_tokens,
            padding_strategy=padding_strategy,
            truncation_strategy=truncation_strategy,
            max_length=max_length,
            stride=stride,
            pad_to_multiple_of=pad_to_multiple_of,
            return_attention_mask=return_attention_mask,
            return_token_type_ids=return_token_type_ids,
            return_overflowing_tokens=return_overflowing_tokens,
            return_special_tokens_mask=return_special_tokens_mask,
            return_length=return_length,
            return_tensors=return_tensors,
            verbose=verbose,
        )

        return BatchEncoding(batch_outputs)

    @add_end_docstrings(ENCODE_KWARGS_DOCSTRING, ENCODE_PLUS_ADDITIONAL_KWARGS_DOCSTRING)
    def _batch_prepare_for_model(
        self,
        batch_ids_pairs: List[Union[PreTokenizedInputPair, Tuple[List[int], None]]],
        add_special_tokens: bool = True,
        padding_strategy: PaddingStrategy = PaddingStrategy.DO_NOT_PAD,
        truncation_strategy: TruncationStrategy = TruncationStrategy.DO_NOT_TRUNCATE,
        max_length: Optional[int] = None,
        stride: int = 0,
        pad_to_multiple_of: Optional[int] = None,
        return_tensors: Optional[str] = None,
        return_token_type_ids: Optional[bool] = None,
        return_attention_mask: Optional[bool] = None,
        return_overflowing_tokens: bool = False,
        return_special_tokens_mask: bool = False,
        return_length: bool = False,
        verbose: bool = True,
    ) -> BatchEncoding:
        """
        Prepares a sequence of input id, or a pair of sequences of inputs ids so that it can be used by the model. It
        adds special tokens, truncates sequences if overflowing while taking into account the special tokens and
        manages a moving window (with user defined stride) for overflowing tokens

        Args:
            batch_ids_pairs: list of tokenized input ids or input ids pairs
        """

        batch_outputs = {}
        for first_ids, second_ids in batch_ids_pairs:
            outputs = self.prepare_for_model(
                first_ids,
                second_ids,
                add_special_tokens=add_special_tokens,
                padding=PaddingStrategy.DO_NOT_PAD.value,  # we pad in batch afterward
                truncation=truncation_strategy.value,
                max_length=max_length,
                stride=stride,
                pad_to_multiple_of=None,  # we pad in batch afterward
                return_attention_mask=False,  # we pad in batch afterward
                return_token_type_ids=return_token_type_ids,
                return_overflowing_tokens=return_overflowing_tokens,
                return_special_tokens_mask=return_special_tokens_mask,
                return_length=return_length,
                return_tensors=None,  # We convert the whole batch to tensors at the end
                prepend_batch_axis=False,
                verbose=verbose,
            )

            for key, value in outputs.items():
                if key not in batch_outputs:
                    batch_outputs[key] = []
                batch_outputs[key].append(value)

        batch_outputs = self.pad(
            batch_outputs,
            padding=padding_strategy.value,
            max_length=max_length,
            pad_to_multiple_of=pad_to_multiple_of,
            return_attention_mask=return_attention_mask,
        )

        batch_outputs = BatchEncoding(batch_outputs, tensor_type=return_tensors)

        return batch_outputs

    def prepare_for_tokenization(
        self, text: str, is_split_into_words: bool = False, **kwargs
    ) -> Tuple[str, Dict[str, Any]]:
        """
        Performs any necessary transformations before tokenization.

        This method should pop the arguments from kwargs and return the remaining `kwargs` as well. We test the
        `kwargs` at the end of the encoding process to be sure all the arguments have been used.

        Args:
            text (`str`):
                The text to prepare.
            is_split_into_words (`bool`, *optional*, defaults to `False`):
                Whether or not the input is already pre-tokenized (e.g., split into words). If set to `True`, the
                tokenizer assumes the input is already split into words (for instance, by splitting it on whitespace)
                which it will tokenize. This is useful for NER or token classification.
            kwargs (`Dict[str, Any]`, *optional*):
                Keyword arguments to use for the tokenization.

        Returns:
            `Tuple[str, Dict[str, Any]]`: The prepared text and the unused kwargs.
        """
        return (text, kwargs)

    def get_special_tokens_mask(
        self, token_ids_0: List, token_ids_1: Optional[List] = None, already_has_special_tokens: bool = False
    ) -> List[int]:
        """
        Retrieves sequence ids from a token list that has no special tokens added. This method is called when adding
        special tokens using the tokenizer `prepare_for_model` or `encode_plus` methods.

        Args:
            token_ids_0 (`List[int]`):
                List of ids of the first sequence.
            token_ids_1 (`List[int]`, *optional*):
                List of ids of the second sequence.
            already_has_special_tokens (`bool`, *optional*, defaults to `False`):
                Whether or not the token list is already formatted with special tokens for the model.

        Returns:
            A list of integers in the range [0, 1]: 1 for a special token, 0 for a sequence token.
        """
        if already_has_special_tokens:
            if token_ids_1 is not None:
                raise ValueError(
                    "You should not supply a second sequence if the provided sequence of "
                    "ids is already formatted with special tokens for the model."
                )

            return super().get_special_tokens_mask(
                token_ids_0=token_ids_0, token_ids_1=token_ids_1, already_has_special_tokens=True
            )
        return [0] * ((len(token_ids_1) if token_ids_1 else 0) + len(token_ids_0))

    @overload
    def convert_ids_to_tokens(self, ids: int, skip_special_tokens: bool = False) -> str:
        ...

    @overload
    def convert_ids_to_tokens(self, ids: List[int], skip_special_tokens: bool = False) -> List[str]:
        ...

    def convert_ids_to_tokens(
        self, ids: Union[int, List[int]], skip_special_tokens: bool = False
    ) -> Union[str, List[str]]:
        """
        Converts a single index or a sequence of indices in a token or a sequence of tokens, using the vocabulary and
        added tokens.

        Args:
            ids (`int` or `List[int]`):
                The token id (or token ids) to convert to tokens.
            skip_special_tokens (`bool`, *optional*, defaults to `False`):
                Whether or not to remove special tokens in the decoding.

        Returns:
            `str` or `List[str]`: The decoded token(s).
        """
        if isinstance(ids, int):
            if ids in self.added_tokens_decoder:
                return self.added_tokens_decoder[ids]
            else:
                return self._convert_id_to_token(ids)
        tokens = []
        for index in ids:
            index = int(index)
            if skip_special_tokens and index in self.all_special_ids:
                continue
            if index in self.added_tokens_decoder:
                tokens.append(self.added_tokens_decoder[index])
            else:
                tokens.append(self._convert_id_to_token(index))
        return tokens

    def _convert_id_to_token(self, index: int) -> str:
        raise NotImplementedError

    def convert_tokens_to_string(self, tokens: List[str]) -> str:
        return " ".join(tokens)

    def _decode(
        self,
        token_ids: List[int],
        skip_special_tokens: bool = False,
        clean_up_tokenization_spaces: bool = None,
        spaces_between_special_tokens: bool = True,
        **kwargs,
    ) -> str:
        self._decode_use_source_tokenizer = kwargs.pop("use_source_tokenizer", False)

        filtered_tokens = self.convert_ids_to_tokens(token_ids, skip_special_tokens=skip_special_tokens)

        # To avoid mixing byte-level and unicode for byte-level BPT
        # we need to build string separately for added tokens and byte-level tokens
        # cf. https://github.com/huggingface/transformers/issues/1133
        sub_texts = []
        current_sub_text = []
        for token in filtered_tokens:
            if skip_special_tokens and token in self.all_special_ids:
                continue
            if token in self.added_tokens_encoder:
                if current_sub_text:
                    sub_texts.append(self.convert_tokens_to_string(current_sub_text))
                    current_sub_text = []
                sub_texts.append(token)
            else:
                current_sub_text.append(token)
        if current_sub_text:
            sub_texts.append(self.convert_tokens_to_string(current_sub_text))

        if spaces_between_special_tokens:
            text = " ".join(sub_texts)
        else:
            text = "".join(sub_texts)

        clean_up_tokenization_spaces = (
            clean_up_tokenization_spaces
            if clean_up_tokenization_spaces is not None
            else self.clean_up_tokenization_spaces
        )
        if clean_up_tokenization_spaces:
            clean_text = self.clean_up_tokenization(text)
            return clean_text
        else:
            return text