tokenization_canine.py

# coding=utf-8
# Copyright Google AI and The HuggingFace Inc. team. All rights reserved.
#
# 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 CANINE."""

from typing import Dict, List, Optional

from ...tokenization_utils import AddedToken, PreTrainedTokenizer
from ...utils import logging


logger = logging.get_logger(__name__)


PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES = {
    "nielsr/canine-s": 2048,
}

# Unicode defines 1,114,112 total “codepoints”
UNICODE_VOCAB_SIZE = 1114112

# Below: Constants defining canonical codepoints for special, pseudo-characters.
# Copied from https://github.com/google-research/language/blob/master/language/canine/special_codepoints.py
PAD = 0

CLS = 0xE000
SEP = 0xE001
BOS = 0xE002
MASK = 0xE003
RESERVED = 0xE004

# Maps special codepoints to human-readable names.
SPECIAL_CODEPOINTS: Dict[int, str] = {
    # Special symbols are represented using codepoints values that are valid,
    # but designated as "Private Use", meaning that they will never be assigned
    # characters by the Unicode Consortium, and are thus safe for use here.
    #
    # NOTE: Do *NOT* add any sort of [UNK_CHAR] here. They are explicitly
    # excluded and should fail with a hard error.
    CLS: "[CLS]",
    SEP: "[SEP]",
    BOS: "[BOS]",
    MASK: "[MASK]",
    PAD: "[PAD]",
    RESERVED: "[RESERVED]",
}

# Maps special codepoint human-readable names to their codepoint values.
SPECIAL_CODEPOINTS_BY_NAME: Dict[str, int] = {name: codepoint for codepoint, name in SPECIAL_CODEPOINTS.items()}


class CanineTokenizer(PreTrainedTokenizer):
    r"""
    Construct a CANINE tokenizer (i.e. a character splitter). It turns text into a sequence of characters, and then
    converts each character into its Unicode code point.

    [`CanineTokenizer`] inherits from [`PreTrainedTokenizer`].

    Refer to superclass [`PreTrainedTokenizer`] for usage examples and documentation concerning parameters.

    Args:
        model_max_length (`int`, *optional*, defaults to 2048):
                The maximum sentence length the model accepts.
    """

    max_model_input_sizes = PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES

    def __init__(
        self,
        bos_token=chr(CLS),
        eos_token=chr(SEP),
        sep_token=chr(SEP),
        cls_token=chr(CLS),
        pad_token=chr(PAD),
        mask_token=chr(MASK),
        add_prefix_space=False,
        model_max_length=2048,
        **kwargs
    ):
        bos_token = AddedToken(bos_token, lstrip=False, rstrip=False) if isinstance(bos_token, str) else bos_token
        eos_token = AddedToken(eos_token, lstrip=False, rstrip=False) if isinstance(eos_token, str) else eos_token
        sep_token = AddedToken(sep_token, lstrip=False, rstrip=False) if isinstance(sep_token, str) else sep_token
        cls_token = AddedToken(cls_token, lstrip=False, rstrip=False) if isinstance(cls_token, str) else cls_token
        pad_token = AddedToken(pad_token, lstrip=False, rstrip=False) if isinstance(pad_token, str) else pad_token

        # Mask token behave like a normal word, i.e. include the space before it
        mask_token = AddedToken(mask_token, lstrip=True, rstrip=False) if isinstance(mask_token, str) else mask_token

        super().__init__(
            bos_token=bos_token,
            eos_token=eos_token,
            sep_token=sep_token,
            cls_token=cls_token,
            pad_token=pad_token,
            mask_token=mask_token,
            add_prefix_space=add_prefix_space,
            model_max_length=model_max_length,
            **kwargs,
        )

        # Creates a mapping for looking up the IDs of special symbols.
        self._special_codepoints: Dict[str, int] = {}
        for codepoint, name in SPECIAL_CODEPOINTS.items():
            self._special_codepoints[name] = codepoint

        # Creates a mapping for looking up the string forms of special symbol IDs.
        self._special_codepoint_strings: Dict[int, str] = {
            codepoint: name for name, codepoint in self._special_codepoints.items()
        }

        self._unicode_vocab_size = UNICODE_VOCAB_SIZE
        self._num_special_tokens = len(self._special_codepoints)

    @property
    def vocab_size(self) -> int:
        return self._unicode_vocab_size

    def _tokenize(self, text: str) -> List[str]:
        """Tokenize a string (i.e. perform character splitting)."""
        return list(text)

    def _convert_token_to_id(self, token: str) -> int:
        """Converts a token (i.e. a Unicode character) in an id (i.e. its integer Unicode code point value)."""
        try:
            return ord(token)
        except TypeError:
            raise ValueError(f"invalid token: '{token}'")

    def _convert_id_to_token(self, index: int) -> str:
        """
        Converts a Unicode code point (integer) in a token (str). In case it's a special code point, convert to
        human-readable format.
        """
        try:
            if index in SPECIAL_CODEPOINTS:
                return SPECIAL_CODEPOINTS[index]
            return chr(index)
        except TypeError:
            raise ValueError(f"invalid id: {index}")

    def convert_tokens_to_string(self, tokens):
        return "".join(tokens)

    def build_inputs_with_special_tokens(
        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None
    ) -> List[int]:
        """
        Build model inputs from a sequence or a pair of sequence for sequence classification tasks by concatenating and
        adding special tokens. A CANINE sequence has the following format:

        - single sequence: `[CLS] X [SEP]`
        - pair of sequences: `[CLS] A [SEP] B [SEP]`

        Args:
            token_ids_0 (`List[int]`):
                List of IDs to which the special tokens will be added.
            token_ids_1 (`List[int]`, *optional*):
                Optional second list of IDs for sequence pairs.

        Returns:
            `List[int]`: List of [input IDs](../glossary#input-ids) with the appropriate special tokens.
        """
        sep = [self.sep_token_id]
        cls = [self.cls_token_id]

        result = cls + token_ids_0 + sep
        if token_ids_1 is not None:
            result += token_ids_1 + sep
        return result

    def get_special_tokens_mask(
        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None, already_has_special_tokens: bool = False
    ) -> List[int]:
        """
        Retrieve 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` method.

        Args:
            token_ids_0 (`List[int]`):
                List of IDs.
            token_ids_1 (`List[int]`, *optional*):
                Optional second list of IDs for sequence pairs.
            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:
            `List[int]`: A list of integers in the range [0, 1]: 1 for a special token, 0 for a sequence token.
        """
        if already_has_special_tokens:
            return super().get_special_tokens_mask(
                token_ids_0=token_ids_0, token_ids_1=token_ids_1, already_has_special_tokens=True
            )

        result = [1] + ([0] * len(token_ids_0)) + [1]
        if token_ids_1 is not None:
            result += ([0] * len(token_ids_1)) + [1]
        return result

    def create_token_type_ids_from_sequences(
        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None
    ) -> List[int]:
        """
        Create a mask from the two sequences passed to be used in a sequence-pair classification task. A CANINE
        sequence pair mask has the following format:

        ```
        0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1
        | first sequence    | second sequence |
        ```

        If `token_ids_1` is `None`, this method only returns the first portion of the mask (0s).

        Args:
            token_ids_0 (`List[int]`):
                List of IDs.
            token_ids_1 (`List[int]`, *optional*):
                Optional second list of IDs for sequence pairs.

        Returns:
            `List[int]`: List of [token type IDs](../glossary#token-type-ids) according to the given sequence(s).
        """
        sep = [self.sep_token_id]
        cls = [self.cls_token_id]

        result = len(cls + token_ids_0 + sep) * [0]
        if token_ids_1 is not None:
            result += len(token_ids_1 + sep) * [1]
        return result

    # CanineTokenizer has no vocab file
    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None):
        return ()