modeling_canine.py

# coding=utf-8
# Copyright 2021 Google AI 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.
""" PyTorch CANINE model."""


import copy
import math
import os
from dataclasses import dataclass
from typing import Optional, Tuple, Union

import torch
import torch.utils.checkpoint
from torch import nn
from torch.nn import BCEWithLogitsLoss, CrossEntropyLoss, MSELoss

from ...activations import ACT2FN
from ...modeling_outputs import (
    BaseModelOutput,
    ModelOutput,
    MultipleChoiceModelOutput,
    QuestionAnsweringModelOutput,
    SequenceClassifierOutput,
    TokenClassifierOutput,
)
from ...modeling_utils import PreTrainedModel
from ...pytorch_utils import apply_chunking_to_forward, find_pruneable_heads_and_indices, prune_linear_layer
from ...utils import (
    add_code_sample_docstrings,
    add_start_docstrings,
    add_start_docstrings_to_model_forward,
    logging,
    replace_return_docstrings,
)
from .configuration_canine import CanineConfig


logger = logging.get_logger(__name__)

_CHECKPOINT_FOR_DOC = "google/canine-s"
_CONFIG_FOR_DOC = "CanineConfig"

CANINE_PRETRAINED_MODEL_ARCHIVE_LIST = [
    "google/canine-s",
    "google/canine-r"
    # See all CANINE models at https://huggingface.co/models?filter=canine
]

# Support up to 16 hash functions.
_PRIMES = [31, 43, 59, 61, 73, 97, 103, 113, 137, 149, 157, 173, 181, 193, 211, 223]


@dataclass
class CanineModelOutputWithPooling(ModelOutput):
    """
    Output type of [`CanineModel`]. Based on [`~modeling_outputs.BaseModelOutputWithPooling`], but with slightly
    different `hidden_states` and `attentions`, as these also include the hidden states and attentions of the shallow
    Transformer encoders.

    Args:
        last_hidden_state (`torch.FloatTensor` of shape `(batch_size, sequence_length, hidden_size)`):
            Sequence of hidden-states at the output of the last layer of the model (i.e. the output of the final
            shallow Transformer encoder).
        pooler_output (`torch.FloatTensor` of shape `(batch_size, hidden_size)`):
            Hidden-state of the first token of the sequence (classification token) at the last layer of the deep
            Transformer encoder, further processed by a Linear layer and a Tanh activation function. The Linear layer
            weights are trained from the next sentence prediction (classification) objective during pretraining.
        hidden_states (`tuple(torch.FloatTensor)`, *optional*, returned when `output_hidden_states=True` is passed or when `config.output_hidden_states=True`):
            Tuple of `torch.FloatTensor` (one for the input to each encoder + one for the output of each layer of each
            encoder) of shape `(batch_size, sequence_length, hidden_size)` and `(batch_size, sequence_length //
            config.downsampling_rate, hidden_size)`. Hidden-states of the model at the output of each layer plus the
            initial input to each Transformer encoder. The hidden states of the shallow encoders have length
            `sequence_length`, but the hidden states of the deep encoder have length `sequence_length` //
            `config.downsampling_rate`.
        attentions (`tuple(torch.FloatTensor)`, *optional*, returned when `output_attentions=True` is passed or when `config.output_attentions=True`):
            Tuple of `torch.FloatTensor` (one for each layer) of the 3 Transformer encoders of shape `(batch_size,
            num_heads, sequence_length, sequence_length)` and `(batch_size, num_heads, sequence_length //
            config.downsampling_rate, sequence_length // config.downsampling_rate)`. Attentions weights after the
            attention softmax, used to compute the weighted average in the self-attention heads.
    """

    last_hidden_state: torch.FloatTensor = None
    pooler_output: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None
    attentions: Optional[Tuple[torch.FloatTensor]] = None


def load_tf_weights_in_canine(model, config, tf_checkpoint_path):
    """Load tf checkpoints in a pytorch model."""
    try:
        import re

        import numpy as np
        import tensorflow as tf
    except ImportError:
        logger.error(
            "Loading a TensorFlow model in PyTorch, requires TensorFlow to be installed. Please see "
            "https://www.tensorflow.org/install/ for installation instructions."
        )
        raise
    tf_path = os.path.abspath(tf_checkpoint_path)
    logger.info(f"Converting TensorFlow checkpoint from {tf_path}")
    # Load weights from TF model
    init_vars = tf.train.list_variables(tf_path)
    names = []
    arrays = []
    for name, shape in init_vars:
        logger.info(f"Loading TF weight {name} with shape {shape}")
        array = tf.train.load_variable(tf_path, name)
        names.append(name)
        arrays.append(array)

    for name, array in zip(names, arrays):
        name = name.split("/")
        # adam_v and adam_m are variables used in AdamWeightDecayOptimizer to calculated m and v
        # which are not required for using pretrained model
        # also discard the cls weights (which were used for the next sentence prediction pre-training task)
        if any(
            n
            in [
                "adam_v",
                "adam_m",
                "AdamWeightDecayOptimizer",
                "AdamWeightDecayOptimizer_1",
                "global_step",
                "cls",
                "autoregressive_decoder",
                "char_output_weights",
            ]
            for n in name
        ):
            logger.info(f"Skipping {'/'.join(name)}")
            continue
        # if first scope name starts with "bert", change it to "encoder"
        if name[0] == "bert":
            name[0] = "encoder"
        # remove "embeddings" middle name of HashBucketCodepointEmbedders
        elif name[1] == "embeddings":
            name.remove(name[1])
        # rename segment_embeddings to token_type_embeddings
        elif name[1] == "segment_embeddings":
            name[1] = "token_type_embeddings"
        # rename initial convolutional projection layer
        elif name[1] == "initial_char_encoder":
            name = ["chars_to_molecules"] + name[-2:]
        # rename final convolutional projection layer
        elif name[0] == "final_char_encoder" and name[1] in ["LayerNorm", "conv"]:
            name = ["projection"] + name[1:]
        pointer = model
        for m_name in name:
            if (re.fullmatch(r"[A-Za-z]+_\d+", m_name)) and "Embedder" not in m_name:
                scope_names = re.split(r"_(\d+)", m_name)
            else:
                scope_names = [m_name]
            if scope_names[0] == "kernel" or scope_names[0] == "gamma":
                pointer = getattr(pointer, "weight")
            elif scope_names[0] == "output_bias" or scope_names[0] == "beta":
                pointer = getattr(pointer, "bias")
            elif scope_names[0] == "output_weights":
                pointer = getattr(pointer, "weight")
            else:
                try:
                    pointer = getattr(pointer, scope_names[0])
                except AttributeError:
                    logger.info(f"Skipping {'/'.join(name)}")
                    continue
            if len(scope_names) >= 2:
                num = int(scope_names[1])
                pointer = pointer[num]
        if m_name[-11:] == "_embeddings":
            pointer = getattr(pointer, "weight")
        elif m_name[-10:] in [f"Embedder_{i}" for i in range(8)]:
            pointer = getattr(pointer, "weight")
        elif m_name == "kernel":
            array = np.transpose(array)

        if pointer.shape != array.shape:
            raise ValueError(f"Pointer shape {pointer.shape} and array shape {array.shape} mismatched")

        logger.info(f"Initialize PyTorch weight {name}")
        pointer.data = torch.from_numpy(array)
    return model


class CanineEmbeddings(nn.Module):
    """Construct the character, position and token_type embeddings."""

    def __init__(self, config):
        super().__init__()

        self.config = config

        # character embeddings
        shard_embedding_size = config.hidden_size // config.num_hash_functions
        for i in range(config.num_hash_functions):
            name = f"HashBucketCodepointEmbedder_{i}"
            setattr(self, name, nn.Embedding(config.num_hash_buckets, shard_embedding_size))
        self.char_position_embeddings = nn.Embedding(config.num_hash_buckets, config.hidden_size)
        self.token_type_embeddings = nn.Embedding(config.type_vocab_size, config.hidden_size)

        # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
        # any TensorFlow checkpoint file
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)

        # position_ids (1, len position emb) is contiguous in memory and exported when serialized
        self.register_buffer(
            "position_ids", torch.arange(config.max_position_embeddings).expand((1, -1)), persistent=False
        )
        self.position_embedding_type = getattr(config, "position_embedding_type", "absolute")

    def _hash_bucket_tensors(self, input_ids, num_hashes: int, num_buckets: int):
        """
        Converts ids to hash bucket ids via multiple hashing.

        Args:
            input_ids: The codepoints or other IDs to be hashed.
            num_hashes: The number of hash functions to use.
            num_buckets: The number of hash buckets (i.e. embeddings in each table).

        Returns:
            A list of tensors, each of which is the hash bucket IDs from one hash function.
        """
        if num_hashes > len(_PRIMES):
            raise ValueError(f"`num_hashes` must be <= {len(_PRIMES)}")

        primes = _PRIMES[:num_hashes]

        result_tensors = []
        for prime in primes:
            hashed = ((input_ids + 1) * prime) % num_buckets
            result_tensors.append(hashed)
        return result_tensors

    def _embed_hash_buckets(self, input_ids, embedding_size: int, num_hashes: int, num_buckets: int):
        """Converts IDs (e.g. codepoints) into embeddings via multiple hashing."""
        if embedding_size % num_hashes != 0:
            raise ValueError(f"Expected `embedding_size` ({embedding_size}) % `num_hashes` ({num_hashes}) == 0")

        hash_bucket_tensors = self._hash_bucket_tensors(input_ids, num_hashes=num_hashes, num_buckets=num_buckets)
        embedding_shards = []
        for i, hash_bucket_ids in enumerate(hash_bucket_tensors):
            name = f"HashBucketCodepointEmbedder_{i}"
            shard_embeddings = getattr(self, name)(hash_bucket_ids)
            embedding_shards.append(shard_embeddings)

        return torch.cat(embedding_shards, dim=-1)

    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
    ) -> torch.FloatTensor:
        if input_ids is not None:
            input_shape = input_ids.size()
        else:
            input_shape = inputs_embeds.size()[:-1]

        seq_length = input_shape[1]

        if position_ids is None:
            position_ids = self.position_ids[:, :seq_length]

        if token_type_ids is None:
            token_type_ids = torch.zeros(input_shape, dtype=torch.long, device=self.position_ids.device)

        if inputs_embeds is None:
            inputs_embeds = self._embed_hash_buckets(
                input_ids, self.config.hidden_size, self.config.num_hash_functions, self.config.num_hash_buckets
            )

        token_type_embeddings = self.token_type_embeddings(token_type_ids)

        embeddings = inputs_embeds + token_type_embeddings

        if self.position_embedding_type == "absolute":
            position_embeddings = self.char_position_embeddings(position_ids)
            embeddings += position_embeddings
        embeddings = self.LayerNorm(embeddings)
        embeddings = self.dropout(embeddings)
        return embeddings


class CharactersToMolecules(nn.Module):
    """Convert character sequence to initial molecule sequence (i.e. downsample) using strided convolutions."""

    def __init__(self, config):
        super().__init__()

        self.conv = nn.Conv1d(
            in_channels=config.hidden_size,
            out_channels=config.hidden_size,
            kernel_size=config.downsampling_rate,
            stride=config.downsampling_rate,
        )
        self.activation = ACT2FN[config.hidden_act]

        # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
        # any TensorFlow checkpoint file
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)

    def forward(self, char_encoding: torch.Tensor) -> torch.Tensor:
        # `cls_encoding`: [batch, 1, hidden_size]
        cls_encoding = char_encoding[:, 0:1, :]

        # char_encoding has shape [batch, char_seq, hidden_size]
        # We transpose it to be [batch, hidden_size, char_seq]
        char_encoding = torch.transpose(char_encoding, 1, 2)
        downsampled = self.conv(char_encoding)
        downsampled = torch.transpose(downsampled, 1, 2)
        downsampled = self.activation(downsampled)

        # Truncate the last molecule in order to reserve a position for [CLS].
        # Often, the last position is never used (unless we completely fill the
        # text buffer). This is important in order to maintain alignment on TPUs
        # (i.e. a multiple of 128).
        downsampled_truncated = downsampled[:, 0:-1, :]

        # We also keep [CLS] as a separate sequence position since we always
        # want to reserve a position (and the model capacity that goes along
        # with that) in the deep BERT stack.
        # `result`: [batch, molecule_seq, molecule_dim]
        result = torch.cat([cls_encoding, downsampled_truncated], dim=1)

        result = self.LayerNorm(result)

        return result


class ConvProjection(nn.Module):
    """
    Project representations from hidden_size*2 back to hidden_size across a window of w = config.upsampling_kernel_size
    characters.
    """

    def __init__(self, config):
        super().__init__()
        self.config = config
        self.conv = nn.Conv1d(
            in_channels=config.hidden_size * 2,
            out_channels=config.hidden_size,
            kernel_size=config.upsampling_kernel_size,
            stride=1,
        )
        self.activation = ACT2FN[config.hidden_act]
        # self.LayerNorm is not snake-cased to stick with TensorFlow model variable name and be able to load
        # any TensorFlow checkpoint file
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)

    def forward(
        self,
        inputs: torch.Tensor,
        final_seq_char_positions: Optional[torch.Tensor] = None,
    ) -> torch.Tensor:
        # inputs has shape [batch, mol_seq, molecule_hidden_size+char_hidden_final]
        # we transpose it to be [batch, molecule_hidden_size+char_hidden_final, mol_seq]
        inputs = torch.transpose(inputs, 1, 2)

        # PyTorch < 1.9 does not support padding="same" (which is used in the original implementation),
        # so we pad the tensor manually before passing it to the conv layer
        # based on https://github.com/google-research/big_transfer/blob/49afe42338b62af9fbe18f0258197a33ee578a6b/bit_tf2/models.py#L36-L38
        pad_total = self.config.upsampling_kernel_size - 1
        pad_beg = pad_total // 2
        pad_end = pad_total - pad_beg

        pad = nn.ConstantPad1d((pad_beg, pad_end), 0)
        # `result`: shape (batch_size, char_seq_len, hidden_size)
        result = self.conv(pad(inputs))
        result = torch.transpose(result, 1, 2)
        result = self.activation(result)
        result = self.LayerNorm(result)
        result = self.dropout(result)
        final_char_seq = result

        if final_seq_char_positions is not None:
            # Limit transformer query seq and attention mask to these character
            # positions to greatly reduce the compute cost. Typically, this is just
            # done for the MLM training task.
            # TODO add support for MLM
            raise NotImplementedError("CanineForMaskedLM is currently not supported")
        else:
            query_seq = final_char_seq

        return query_seq


class CanineSelfAttention(nn.Module):
    def __init__(self, config):
        super().__init__()
        if config.hidden_size % config.num_attention_heads != 0 and not hasattr(config, "embedding_size"):
            raise ValueError(
                f"The hidden size ({config.hidden_size}) is not a multiple of the number of attention "
                f"heads ({config.num_attention_heads})"
            )

        self.num_attention_heads = config.num_attention_heads
        self.attention_head_size = int(config.hidden_size / config.num_attention_heads)
        self.all_head_size = self.num_attention_heads * self.attention_head_size

        self.query = nn.Linear(config.hidden_size, self.all_head_size)
        self.key = nn.Linear(config.hidden_size, self.all_head_size)
        self.value = nn.Linear(config.hidden_size, self.all_head_size)

        self.dropout = nn.Dropout(config.attention_probs_dropout_prob)
        self.position_embedding_type = getattr(config, "position_embedding_type", "absolute")
        if self.position_embedding_type == "relative_key" or self.position_embedding_type == "relative_key_query":
            self.max_position_embeddings = config.max_position_embeddings
            self.distance_embedding = nn.Embedding(2 * config.max_position_embeddings - 1, self.attention_head_size)

    def transpose_for_scores(self, x):
        new_x_shape = x.size()[:-1] + (self.num_attention_heads, self.attention_head_size)
        x = x.view(*new_x_shape)
        return x.permute(0, 2, 1, 3)

    def forward(
        self,
        from_tensor: torch.Tensor,
        to_tensor: torch.Tensor,
        attention_mask: Optional[torch.FloatTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        output_attentions: Optional[bool] = False,
    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
        mixed_query_layer = self.query(from_tensor)

        # If this is instantiated as a cross-attention module, the keys
        # and values come from an encoder; the attention mask needs to be
        # such that the encoder's padding tokens are not attended to.

        key_layer = self.transpose_for_scores(self.key(to_tensor))
        value_layer = self.transpose_for_scores(self.value(to_tensor))

        query_layer = self.transpose_for_scores(mixed_query_layer)

        # Take the dot product between "query" and "key" to get the raw attention scores.
        attention_scores = torch.matmul(query_layer, key_layer.transpose(-1, -2))

        if self.position_embedding_type == "relative_key" or self.position_embedding_type == "relative_key_query":
            seq_length = from_tensor.size()[1]
            position_ids_l = torch.arange(seq_length, dtype=torch.long, device=from_tensor.device).view(-1, 1)
            position_ids_r = torch.arange(seq_length, dtype=torch.long, device=from_tensor.device).view(1, -1)
            distance = position_ids_l - position_ids_r
            positional_embedding = self.distance_embedding(distance + self.max_position_embeddings - 1)
            positional_embedding = positional_embedding.to(dtype=query_layer.dtype)  # fp16 compatibility

            if self.position_embedding_type == "relative_key":
                relative_position_scores = torch.einsum("bhld,lrd->bhlr", query_layer, positional_embedding)
                attention_scores = attention_scores + relative_position_scores
            elif self.position_embedding_type == "relative_key_query":
                relative_position_scores_query = torch.einsum("bhld,lrd->bhlr", query_layer, positional_embedding)
                relative_position_scores_key = torch.einsum("bhrd,lrd->bhlr", key_layer, positional_embedding)
                attention_scores = attention_scores + relative_position_scores_query + relative_position_scores_key

        attention_scores = attention_scores / math.sqrt(self.attention_head_size)
        if attention_mask is not None:
            if attention_mask.ndim == 3:
                # if attention_mask is 3D, do the following:
                attention_mask = torch.unsqueeze(attention_mask, dim=1)
                # Since attention_mask is 1.0 for positions we want to attend and 0.0 for
                # masked positions, this operation will create a tensor which is 0.0 for
                # positions we want to attend and the dtype's smallest value for masked positions.
                attention_mask = (1.0 - attention_mask.float()) * torch.finfo(attention_scores.dtype).min
            # Apply the attention mask (precomputed for all layers in CanineModel forward() function)
            attention_scores = attention_scores + attention_mask

        # Normalize the attention scores to probabilities.
        attention_probs = nn.functional.softmax(attention_scores, dim=-1)

        # This is actually dropping out entire tokens to attend to, which might
        # seem a bit unusual, but is taken from the original Transformer paper.
        attention_probs = self.dropout(attention_probs)

        # Mask heads if we want to
        if head_mask is not None:
            attention_probs = attention_probs * head_mask

        context_layer = torch.matmul(attention_probs, value_layer)

        context_layer = context_layer.permute(0, 2, 1, 3).contiguous()
        new_context_layer_shape = context_layer.size()[:-2] + (self.all_head_size,)
        context_layer = context_layer.view(*new_context_layer_shape)

        outputs = (context_layer, attention_probs) if output_attentions else (context_layer,)

        return outputs


class CanineSelfOutput(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.hidden_size, config.hidden_size)
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)

    def forward(
        self, hidden_states: Tuple[torch.FloatTensor], input_tensor: torch.FloatTensor
    ) -> Tuple[torch.FloatTensor, torch.FloatTensor]:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.dropout(hidden_states)
        hidden_states = self.LayerNorm(hidden_states + input_tensor)
        return hidden_states


class CanineAttention(nn.Module):
    """
    Additional arguments related to local attention:

        - **local** (`bool`, *optional*, defaults to `False`) -- Whether to apply local attention.
        - **always_attend_to_first_position** (`bool`, *optional*, defaults to `False`) -- Should all blocks be able to
          attend
        to the `to_tensor`'s first position (e.g. a [CLS] position)? - **first_position_attends_to_all** (`bool`,
        *optional*, defaults to `False`) -- Should the *from_tensor*'s first position be able to attend to all
        positions within the *from_tensor*? - **attend_from_chunk_width** (`int`, *optional*, defaults to 128) -- The
        width of each block-wise chunk in `from_tensor`. - **attend_from_chunk_stride** (`int`, *optional*, defaults to
        128) -- The number of elements to skip when moving to the next block in `from_tensor`. -
        **attend_to_chunk_width** (`int`, *optional*, defaults to 128) -- The width of each block-wise chunk in
        *to_tensor*. - **attend_to_chunk_stride** (`int`, *optional*, defaults to 128) -- The number of elements to
        skip when moving to the next block in `to_tensor`.
    """

    def __init__(
        self,
        config,
        local=False,
        always_attend_to_first_position: bool = False,
        first_position_attends_to_all: bool = False,
        attend_from_chunk_width: int = 128,
        attend_from_chunk_stride: int = 128,
        attend_to_chunk_width: int = 128,
        attend_to_chunk_stride: int = 128,
    ):
        super().__init__()
        self.self = CanineSelfAttention(config)
        self.output = CanineSelfOutput(config)
        self.pruned_heads = set()

        # additional arguments related to local attention
        self.local = local
        if attend_from_chunk_width < attend_from_chunk_stride:
            raise ValueError(
                "`attend_from_chunk_width` < `attend_from_chunk_stride` would cause sequence positions to get skipped."
            )
        if attend_to_chunk_width < attend_to_chunk_stride:
            raise ValueError(
                "`attend_to_chunk_width` < `attend_to_chunk_stride`would cause sequence positions to get skipped."
            )
        self.always_attend_to_first_position = always_attend_to_first_position
        self.first_position_attends_to_all = first_position_attends_to_all
        self.attend_from_chunk_width = attend_from_chunk_width
        self.attend_from_chunk_stride = attend_from_chunk_stride
        self.attend_to_chunk_width = attend_to_chunk_width
        self.attend_to_chunk_stride = attend_to_chunk_stride

    def prune_heads(self, heads):
        if len(heads) == 0:
            return
        heads, index = find_pruneable_heads_and_indices(
            heads, self.self.num_attention_heads, self.self.attention_head_size, self.pruned_heads
        )

        # Prune linear layers
        self.self.query = prune_linear_layer(self.self.query, index)
        self.self.key = prune_linear_layer(self.self.key, index)
        self.self.value = prune_linear_layer(self.self.value, index)
        self.output.dense = prune_linear_layer(self.output.dense, index, dim=1)

        # Update hyper params and store pruned heads
        self.self.num_attention_heads = self.self.num_attention_heads - len(heads)
        self.self.all_head_size = self.self.attention_head_size * self.self.num_attention_heads
        self.pruned_heads = self.pruned_heads.union(heads)

    def forward(
        self,
        hidden_states: Tuple[torch.FloatTensor],
        attention_mask: Optional[torch.FloatTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        output_attentions: Optional[bool] = False,
    ) -> Tuple[torch.FloatTensor, Optional[torch.FloatTensor]]:
        if not self.local:
            self_outputs = self.self(hidden_states, hidden_states, attention_mask, head_mask, output_attentions)
            attention_output = self_outputs[0]
        else:
            from_seq_length = to_seq_length = hidden_states.shape[1]
            from_tensor = to_tensor = hidden_states

            # Create chunks (windows) that we will attend *from* and then concatenate them.
            from_chunks = []
            if self.first_position_attends_to_all:
                from_chunks.append((0, 1))
                # We must skip this first position so that our output sequence is the
                # correct length (this matters in the *from* sequence only).
                from_start = 1
            else:
                from_start = 0
            for chunk_start in range(from_start, from_seq_length, self.attend_from_chunk_stride):
                chunk_end = min(from_seq_length, chunk_start + self.attend_from_chunk_width)
                from_chunks.append((chunk_start, chunk_end))

            # Determine the chunks (windows) that will will attend *to*.
            to_chunks = []
            if self.first_position_attends_to_all:
                to_chunks.append((0, to_seq_length))
            for chunk_start in range(0, to_seq_length, self.attend_to_chunk_stride):
                chunk_end = min(to_seq_length, chunk_start + self.attend_to_chunk_width)
                to_chunks.append((chunk_start, chunk_end))

            if len(from_chunks) != len(to_chunks):
                raise ValueError(
                    f"Expected to have same number of `from_chunks` ({from_chunks}) and "
                    f"`to_chunks` ({from_chunks}). Check strides."
                )

            # next, compute attention scores for each pair of windows and concatenate
            attention_output_chunks = []
            attention_probs_chunks = []
            for (from_start, from_end), (to_start, to_end) in zip(from_chunks, to_chunks):
                from_tensor_chunk = from_tensor[:, from_start:from_end, :]
                to_tensor_chunk = to_tensor[:, to_start:to_end, :]
                # `attention_mask`: <float>[batch_size, from_seq, to_seq]
                # `attention_mask_chunk`: <float>[batch_size, from_seq_chunk, to_seq_chunk]
                attention_mask_chunk = attention_mask[:, from_start:from_end, to_start:to_end]
                if self.always_attend_to_first_position:
                    cls_attention_mask = attention_mask[:, from_start:from_end, 0:1]
                    attention_mask_chunk = torch.cat([cls_attention_mask, attention_mask_chunk], dim=2)

                    cls_position = to_tensor[:, 0:1, :]
                    to_tensor_chunk = torch.cat([cls_position, to_tensor_chunk], dim=1)

                attention_outputs_chunk = self.self(
                    from_tensor_chunk, to_tensor_chunk, attention_mask_chunk, head_mask, output_attentions
                )
                attention_output_chunks.append(attention_outputs_chunk[0])
                if output_attentions:
                    attention_probs_chunks.append(attention_outputs_chunk[1])

            attention_output = torch.cat(attention_output_chunks, dim=1)

        attention_output = self.output(attention_output, hidden_states)
        outputs = (attention_output,)
        if not self.local:
            outputs = outputs + self_outputs[1:]  # add attentions if we output them
        else:
            outputs = outputs + tuple(attention_probs_chunks)  # add attentions if we output them
        return outputs


class CanineIntermediate(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.hidden_size, config.intermediate_size)
        if isinstance(config.hidden_act, str):
            self.intermediate_act_fn = ACT2FN[config.hidden_act]
        else:
            self.intermediate_act_fn = config.hidden_act

    def forward(self, hidden_states: torch.FloatTensor) -> torch.FloatTensor:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.intermediate_act_fn(hidden_states)
        return hidden_states


class CanineOutput(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.intermediate_size, config.hidden_size)
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)

    def forward(self, hidden_states: Tuple[torch.FloatTensor], input_tensor: torch.FloatTensor) -> torch.FloatTensor:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.dropout(hidden_states)
        hidden_states = self.LayerNorm(hidden_states + input_tensor)
        return hidden_states


class CanineLayer(nn.Module):
    def __init__(
        self,
        config,
        local,
        always_attend_to_first_position,
        first_position_attends_to_all,
        attend_from_chunk_width,
        attend_from_chunk_stride,
        attend_to_chunk_width,
        attend_to_chunk_stride,
    ):
        super().__init__()
        self.chunk_size_feed_forward = config.chunk_size_feed_forward
        self.seq_len_dim = 1
        self.attention = CanineAttention(
            config,
            local,
            always_attend_to_first_position,
            first_position_attends_to_all,
            attend_from_chunk_width,
            attend_from_chunk_stride,
            attend_to_chunk_width,
            attend_to_chunk_stride,
        )
        self.intermediate = CanineIntermediate(config)
        self.output = CanineOutput(config)

    def forward(
        self,
        hidden_states: Tuple[torch.FloatTensor],
        attention_mask: Optional[torch.FloatTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        output_attentions: Optional[bool] = False,
    ) -> Tuple[torch.FloatTensor, Optional[torch.FloatTensor]]:
        self_attention_outputs = self.attention(
            hidden_states,
            attention_mask,
            head_mask,
            output_attentions=output_attentions,
        )
        attention_output = self_attention_outputs[0]

        outputs = self_attention_outputs[1:]  # add self attentions if we output attention weights

        layer_output = apply_chunking_to_forward(
            self.feed_forward_chunk, self.chunk_size_feed_forward, self.seq_len_dim, attention_output
        )
        outputs = (layer_output,) + outputs

        return outputs

    def feed_forward_chunk(self, attention_output):
        intermediate_output = self.intermediate(attention_output)
        layer_output = self.output(intermediate_output, attention_output)
        return layer_output


class CanineEncoder(nn.Module):
    def __init__(
        self,
        config,
        local=False,
        always_attend_to_first_position=False,
        first_position_attends_to_all=False,
        attend_from_chunk_width=128,
        attend_from_chunk_stride=128,
        attend_to_chunk_width=128,
        attend_to_chunk_stride=128,
    ):
        super().__init__()
        self.config = config
        self.layer = nn.ModuleList(
            [
                CanineLayer(
                    config,
                    local,
                    always_attend_to_first_position,
                    first_position_attends_to_all,
                    attend_from_chunk_width,
                    attend_from_chunk_stride,
                    attend_to_chunk_width,
                    attend_to_chunk_stride,
                )
                for _ in range(config.num_hidden_layers)
            ]
        )
        self.gradient_checkpointing = False

    def forward(
        self,
        hidden_states: Tuple[torch.FloatTensor],
        attention_mask: Optional[torch.FloatTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        output_attentions: Optional[bool] = False,
        output_hidden_states: Optional[bool] = False,
        return_dict: Optional[bool] = True,
    ) -> Union[Tuple, BaseModelOutput]:
        all_hidden_states = () if output_hidden_states else None
        all_self_attentions = () if output_attentions else None

        for i, layer_module in enumerate(self.layer):
            if output_hidden_states:
                all_hidden_states = all_hidden_states + (hidden_states,)

            layer_head_mask = head_mask[i] if head_mask is not None else None

            if self.gradient_checkpointing and self.training:

                def create_custom_forward(module):
                    def custom_forward(*inputs):
                        return module(*inputs, output_attentions)

                    return custom_forward

                layer_outputs = torch.utils.checkpoint.checkpoint(
                    create_custom_forward(layer_module),
                    hidden_states,
                    attention_mask,
                    layer_head_mask,
                )
            else:
                layer_outputs = layer_module(hidden_states, attention_mask, layer_head_mask, output_attentions)

            hidden_states = layer_outputs[0]
            if output_attentions:
                all_self_attentions = all_self_attentions + (layer_outputs[1],)

        if output_hidden_states:
            all_hidden_states = all_hidden_states + (hidden_states,)

        if not return_dict:
            return tuple(v for v in [hidden_states, all_hidden_states, all_self_attentions] if v is not None)
        return BaseModelOutput(
            last_hidden_state=hidden_states,
            hidden_states=all_hidden_states,
            attentions=all_self_attentions,
        )


class CaninePooler(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.hidden_size, config.hidden_size)
        self.activation = nn.Tanh()

    def forward(self, hidden_states: Tuple[torch.FloatTensor]) -> torch.FloatTensor:
        # We "pool" the model by simply taking the hidden state corresponding
        # to the first token.
        first_token_tensor = hidden_states[:, 0]
        pooled_output = self.dense(first_token_tensor)
        pooled_output = self.activation(pooled_output)
        return pooled_output


class CaninePredictionHeadTransform(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.dense = nn.Linear(config.hidden_size, config.hidden_size)
        if isinstance(config.hidden_act, str):
            self.transform_act_fn = ACT2FN[config.hidden_act]
        else:
            self.transform_act_fn = config.hidden_act
        self.LayerNorm = nn.LayerNorm(config.hidden_size, eps=config.layer_norm_eps)

    def forward(self, hidden_states: Tuple[torch.FloatTensor]) -> torch.FloatTensor:
        hidden_states = self.dense(hidden_states)
        hidden_states = self.transform_act_fn(hidden_states)
        hidden_states = self.LayerNorm(hidden_states)
        return hidden_states


class CanineLMPredictionHead(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.transform = CaninePredictionHeadTransform(config)

        # The output weights are the same as the input embeddings, but there is
        # an output-only bias for each token.
        self.decoder = nn.Linear(config.hidden_size, config.vocab_size, bias=False)

        self.bias = nn.Parameter(torch.zeros(config.vocab_size))

        # Need a link between the two variables so that the bias is correctly resized with `resize_token_embeddings`
        self.decoder.bias = self.bias

    def forward(self, hidden_states: Tuple[torch.FloatTensor]) -> torch.FloatTensor:
        hidden_states = self.transform(hidden_states)
        hidden_states = self.decoder(hidden_states)
        return hidden_states


class CanineOnlyMLMHead(nn.Module):
    def __init__(self, config):
        super().__init__()
        self.predictions = CanineLMPredictionHead(config)

    def forward(
        self,
        sequence_output: Tuple[torch.Tensor],
    ) -> Tuple[torch.Tensor]:
        prediction_scores = self.predictions(sequence_output)
        return prediction_scores


class CaninePreTrainedModel(PreTrainedModel):
    """
    An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
    models.
    """

    config_class = CanineConfig
    load_tf_weights = load_tf_weights_in_canine
    base_model_prefix = "canine"
    supports_gradient_checkpointing = True

    def _init_weights(self, module):
        """Initialize the weights"""
        if isinstance(module, (nn.Linear, nn.Conv1d)):
            # Slightly different from the TF version which uses truncated_normal for initialization
            # cf https://github.com/pytorch/pytorch/pull/5617
            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
            if module.bias is not None:
                module.bias.data.zero_()
        elif isinstance(module, nn.Embedding):
            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
            if module.padding_idx is not None:
                module.weight.data[module.padding_idx].zero_()
        elif isinstance(module, nn.LayerNorm):
            module.bias.data.zero_()
            module.weight.data.fill_(1.0)

    def _set_gradient_checkpointing(self, module, value=False):
        if isinstance(module, CanineEncoder):
            module.gradient_checkpointing = value


CANINE_START_DOCSTRING = r"""
    This model is a PyTorch [torch.nn.Module](https://pytorch.org/docs/stable/nn.html#torch.nn.Module) sub-class. Use
    it as a regular PyTorch Module and refer to the PyTorch documentation for all matter related to general usage and
    behavior.

    Parameters:
        config ([`CanineConfig`]): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the
            configuration. Check out the [`~PreTrainedModel.from_pretrained`] method to load the model weights.
"""

CANINE_INPUTS_DOCSTRING = r"""
    Args:
        input_ids (`torch.LongTensor` of shape `({0})`):
            Indices of input sequence tokens in the vocabulary.

            Indices can be obtained using [`AutoTokenizer`]. See [`PreTrainedTokenizer.encode`] and
            [`PreTrainedTokenizer.__call__`] for details.

            [What are input IDs?](../glossary#input-ids)
        attention_mask (`torch.FloatTensor` of shape `({0})`, *optional*):
            Mask to avoid performing attention on padding token indices. Mask values selected in `[0, 1]`:

            - 1 for tokens that are **not masked**,
            - 0 for tokens that are **masked**.

            [What are attention masks?](../glossary#attention-mask)
        token_type_ids (`torch.LongTensor` of shape `({0})`, *optional*):
            Segment token indices to indicate first and second portions of the inputs. Indices are selected in `[0,
            1]`:

            - 0 corresponds to a *sentence A* token,
            - 1 corresponds to a *sentence B* token.

            [What are token type IDs?](../glossary#token-type-ids)
        position_ids (`torch.LongTensor` of shape `({0})`, *optional*):
            Indices of positions of each input sequence tokens in the position embeddings. Selected in the range `[0,
            config.max_position_embeddings - 1]`.

            [What are position IDs?](../glossary#position-ids)
        head_mask (`torch.FloatTensor` of shape `(num_heads,)` or `(num_layers, num_heads)`, *optional*):
            Mask to nullify selected heads of the self-attention modules. Mask values selected in `[0, 1]`:

            - 1 indicates the head is **not masked**,
            - 0 indicates the head is **masked**.

        inputs_embeds (`torch.FloatTensor` of shape `({0}, hidden_size)`, *optional*):
            Optionally, instead of passing `input_ids` you can choose to directly pass an embedded representation. This
            is useful if you want more control over how to convert *input_ids* indices into associated vectors than the
            model's internal embedding lookup matrix.
        output_attentions (`bool`, *optional*):
            Whether or not to return the attentions tensors of all attention layers. See `attentions` under returned
            tensors for more detail.
        output_hidden_states (`bool`, *optional*):
            Whether or not to return the hidden states of all layers. See `hidden_states` under returned tensors for
            more detail.
        return_dict (`bool`, *optional*):
            Whether or not to return a [`~utils.ModelOutput`] instead of a plain tuple.
"""


@add_start_docstrings(
    "The bare CANINE Model transformer outputting raw hidden-states without any specific head on top.",
    CANINE_START_DOCSTRING,
)
class CanineModel(CaninePreTrainedModel):
    def __init__(self, config, add_pooling_layer=True):
        super().__init__(config)
        self.config = config
        shallow_config = copy.deepcopy(config)
        shallow_config.num_hidden_layers = 1

        self.char_embeddings = CanineEmbeddings(config)
        # shallow/low-dim transformer encoder to get a initial character encoding
        self.initial_char_encoder = CanineEncoder(
            shallow_config,
            local=True,
            always_attend_to_first_position=False,
            first_position_attends_to_all=False,
            attend_from_chunk_width=config.local_transformer_stride,
            attend_from_chunk_stride=config.local_transformer_stride,
            attend_to_chunk_width=config.local_transformer_stride,
            attend_to_chunk_stride=config.local_transformer_stride,
        )
        self.chars_to_molecules = CharactersToMolecules(config)
        # deep transformer encoder
        self.encoder = CanineEncoder(config)
        self.projection = ConvProjection(config)
        # shallow/low-dim transformer encoder to get a final character encoding
        self.final_char_encoder = CanineEncoder(shallow_config)

        self.pooler = CaninePooler(config) if add_pooling_layer else None

        # Initialize weights and apply final processing
        self.post_init()

    def _prune_heads(self, heads_to_prune):
        """
        Prunes heads of the model. heads_to_prune: dict of {layer_num: list of heads to prune in this layer} See base
        class PreTrainedModel
        """
        for layer, heads in heads_to_prune.items():
            self.encoder.layer[layer].attention.prune_heads(heads)

    def _create_3d_attention_mask_from_input_mask(self, from_tensor, to_mask):
        """
        Create 3D attention mask from a 2D tensor mask.

        Args:
            from_tensor: 2D or 3D Tensor of shape [batch_size, from_seq_length, ...].
            to_mask: int32 Tensor of shape [batch_size, to_seq_length].

        Returns:
            float Tensor of shape [batch_size, from_seq_length, to_seq_length].
        """
        batch_size, from_seq_length = from_tensor.shape[0], from_tensor.shape[1]

        to_seq_length = to_mask.shape[1]

        to_mask = torch.reshape(to_mask, (batch_size, 1, to_seq_length)).float()

        # We don't assume that `from_tensor` is a mask (although it could be). We
        # don't actually care if we attend *from* padding tokens (only *to* padding)
        # tokens so we create a tensor of all ones.
        broadcast_ones = torch.ones(size=(batch_size, from_seq_length, 1), dtype=torch.float32, device=to_mask.device)

        # Here we broadcast along two dimensions to create the mask.
        mask = broadcast_ones * to_mask

        return mask

    def _downsample_attention_mask(self, char_attention_mask: torch.Tensor, downsampling_rate: int):
        """Downsample 2D character attention mask to 2D molecule attention mask using MaxPool1d layer."""

        # first, make char_attention_mask 3D by adding a channel dim
        batch_size, char_seq_len = char_attention_mask.shape
        poolable_char_mask = torch.reshape(char_attention_mask, (batch_size, 1, char_seq_len))

        # next, apply MaxPool1d to get pooled_molecule_mask of shape (batch_size, 1, mol_seq_len)
        pooled_molecule_mask = torch.nn.MaxPool1d(kernel_size=downsampling_rate, stride=downsampling_rate)(
            poolable_char_mask.float()
        )

        # finally, squeeze to get tensor of shape (batch_size, mol_seq_len)
        molecule_attention_mask = torch.squeeze(pooled_molecule_mask, dim=-1)

        return molecule_attention_mask

    def _repeat_molecules(self, molecules: torch.Tensor, char_seq_length: torch.Tensor) -> torch.Tensor:
        """Repeats molecules to make them the same length as the char sequence."""

        rate = self.config.downsampling_rate

        molecules_without_extra_cls = molecules[:, 1:, :]
        # `repeated`: [batch_size, almost_char_seq_len, molecule_hidden_size]
        repeated = torch.repeat_interleave(molecules_without_extra_cls, repeats=rate, dim=-2)

        # So far, we've repeated the elements sufficient for any `char_seq_length`
        # that's a multiple of `downsampling_rate`. Now we account for the last
        # n elements (n < `downsampling_rate`), i.e. the remainder of floor
        # division. We do this by repeating the last molecule a few extra times.
        last_molecule = molecules[:, -1:, :]
        remainder_length = torch.fmod(torch.tensor(char_seq_length), torch.tensor(rate)).item()
        remainder_repeated = torch.repeat_interleave(
            last_molecule,
            # +1 molecule to compensate for truncation.
            repeats=remainder_length + rate,
            dim=-2,
        )

        # `repeated`: [batch_size, char_seq_len, molecule_hidden_size]
        return torch.cat([repeated, remainder_repeated], dim=-2)

    @add_start_docstrings_to_model_forward(CANINE_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @add_code_sample_docstrings(
        checkpoint=_CHECKPOINT_FOR_DOC,
        output_type=CanineModelOutputWithPooling,
        config_class=_CONFIG_FOR_DOC,
    )
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.FloatTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, CanineModelOutputWithPooling]:
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        all_hidden_states = () if output_hidden_states else None
        all_self_attentions = () if output_attentions else None
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        if input_ids is not None and inputs_embeds is not None:
            raise ValueError("You cannot specify both input_ids and inputs_embeds at the same time")
        elif input_ids is not None:
            self.warn_if_padding_and_no_attention_mask(input_ids, attention_mask)
            input_shape = input_ids.size()
        elif inputs_embeds is not None:
            input_shape = inputs_embeds.size()[:-1]
        else:
            raise ValueError("You have to specify either input_ids or inputs_embeds")

        batch_size, seq_length = input_shape
        device = input_ids.device if input_ids is not None else inputs_embeds.device

        if attention_mask is None:
            attention_mask = torch.ones(((batch_size, seq_length)), device=device)
        if token_type_ids is None:
            token_type_ids = torch.zeros(input_shape, dtype=torch.long, device=device)

        # We can provide a self-attention mask of dimensions [batch_size, from_seq_length, to_seq_length]
        # ourselves in which case we just need to make it broadcastable to all heads.
        extended_attention_mask: torch.Tensor = self.get_extended_attention_mask(attention_mask, input_shape)
        molecule_attention_mask = self._downsample_attention_mask(
            attention_mask, downsampling_rate=self.config.downsampling_rate
        )
        extended_molecule_attention_mask: torch.Tensor = self.get_extended_attention_mask(
            molecule_attention_mask, (batch_size, molecule_attention_mask.shape[-1])
        )

        # Prepare head mask if needed
        # 1.0 in head_mask indicate we keep the head
        # attention_probs has shape bsz x n_heads x N x N
        # input head_mask has shape [num_heads] or [num_hidden_layers x num_heads]
        # and head_mask is converted to shape [num_hidden_layers x batch x num_heads x seq_length x seq_length]
        head_mask = self.get_head_mask(head_mask, self.config.num_hidden_layers)

        # `input_char_embeddings`: shape (batch_size, char_seq, char_dim)
        input_char_embeddings = self.char_embeddings(
            input_ids=input_ids,
            position_ids=position_ids,
            token_type_ids=token_type_ids,
            inputs_embeds=inputs_embeds,
        )

        # Contextualize character embeddings using shallow Transformer.
        # We use a 3D attention mask for the local attention.
        # `input_char_encoding`: shape (batch_size, char_seq_len, char_dim)
        char_attention_mask = self._create_3d_attention_mask_from_input_mask(
            input_ids if input_ids is not None else inputs_embeds, attention_mask
        )
        init_chars_encoder_outputs = self.initial_char_encoder(
            input_char_embeddings,
            attention_mask=char_attention_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
        )
        input_char_encoding = init_chars_encoder_outputs.last_hidden_state

        # Downsample chars to molecules.
        # The following lines have dimensions: [batch, molecule_seq, molecule_dim].
        # In this transformation, we change the dimensionality from `char_dim` to
        # `molecule_dim`, but do *NOT* add a resnet connection. Instead, we rely on
        # the resnet connections (a) from the final char transformer stack back into
        # the original char transformer stack and (b) the resnet connections from
        # the final char transformer stack back into the deep BERT stack of
        # molecules.
        #
        # Empirically, it is critical to use a powerful enough transformation here:
        # mean pooling causes training to diverge with huge gradient norms in this
        # region of the model; using a convolution here resolves this issue. From
        # this, it seems that molecules and characters require a very different
        # feature space; intuitively, this makes sense.
        init_molecule_encoding = self.chars_to_molecules(input_char_encoding)

        # Deep BERT encoder
        # `molecule_sequence_output`: shape (batch_size, mol_seq_len, mol_dim)
        encoder_outputs = self.encoder(
            init_molecule_encoding,
            attention_mask=extended_molecule_attention_mask,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        molecule_sequence_output = encoder_outputs[0]
        pooled_output = self.pooler(molecule_sequence_output) if self.pooler is not None else None

        # Upsample molecules back to characters.
        # `repeated_molecules`: shape (batch_size, char_seq_len, mol_hidden_size)
        repeated_molecules = self._repeat_molecules(molecule_sequence_output, char_seq_length=input_shape[-1])

        # Concatenate representations (contextualized char embeddings and repeated molecules):
        # `concat`: shape [batch_size, char_seq_len, molecule_hidden_size+char_hidden_final]
        concat = torch.cat([input_char_encoding, repeated_molecules], dim=-1)

        # Project representation dimension back to hidden_size
        # `sequence_output`: shape (batch_size, char_seq_len, hidden_size])
        sequence_output = self.projection(concat)

        # Apply final shallow Transformer
        # `sequence_output`: shape (batch_size, char_seq_len, hidden_size])
        final_chars_encoder_outputs = self.final_char_encoder(
            sequence_output,
            attention_mask=extended_attention_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
        )
        sequence_output = final_chars_encoder_outputs.last_hidden_state

        if output_hidden_states:
            deep_encoder_hidden_states = encoder_outputs.hidden_states if return_dict else encoder_outputs[1]
            all_hidden_states = (
                all_hidden_states
                + init_chars_encoder_outputs.hidden_states
                + deep_encoder_hidden_states
                + final_chars_encoder_outputs.hidden_states
            )

        if output_attentions:
            deep_encoder_self_attentions = encoder_outputs.attentions if return_dict else encoder_outputs[-1]
            all_self_attentions = (
                all_self_attentions
                + init_chars_encoder_outputs.attentions
                + deep_encoder_self_attentions
                + final_chars_encoder_outputs.attentions
            )

        if not return_dict:
            output = (sequence_output, pooled_output)
            output += tuple(v for v in [all_hidden_states, all_self_attentions] if v is not None)
            return output

        return CanineModelOutputWithPooling(
            last_hidden_state=sequence_output,
            pooler_output=pooled_output,
            hidden_states=all_hidden_states,
            attentions=all_self_attentions,
        )


@add_start_docstrings(
    """
    CANINE Model transformer with a sequence classification/regression head on top (a linear layer on top of the pooled
    output) e.g. for GLUE tasks.
    """,
    CANINE_START_DOCSTRING,
)
class CanineForSequenceClassification(CaninePreTrainedModel):
    def __init__(self, config):
        super().__init__(config)
        self.num_labels = config.num_labels

        self.canine = CanineModel(config)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)
        self.classifier = nn.Linear(config.hidden_size, config.num_labels)

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(CANINE_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @add_code_sample_docstrings(
        checkpoint=_CHECKPOINT_FOR_DOC,
        output_type=SequenceClassifierOutput,
        config_class=_CONFIG_FOR_DOC,
    )
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.FloatTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, SequenceClassifierOutput]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size,)`, *optional*):
            Labels for computing the sequence classification/regression loss. Indices should be in `[0, ...,
            config.num_labels - 1]`. If `config.num_labels == 1` a regression loss is computed (Mean-Square loss), If
            `config.num_labels > 1` a classification loss is computed (Cross-Entropy).
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.canine(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        pooled_output = outputs[1]

        pooled_output = self.dropout(pooled_output)
        logits = self.classifier(pooled_output)

        loss = None
        if labels is not None:
            if self.config.problem_type is None:
                if self.num_labels == 1:
                    self.config.problem_type = "regression"
                elif self.num_labels > 1 and (labels.dtype == torch.long or labels.dtype == torch.int):
                    self.config.problem_type = "single_label_classification"
                else:
                    self.config.problem_type = "multi_label_classification"

            if self.config.problem_type == "regression":
                loss_fct = MSELoss()
                if self.num_labels == 1:
                    loss = loss_fct(logits.squeeze(), labels.squeeze())
                else:
                    loss = loss_fct(logits, labels)
            elif self.config.problem_type == "single_label_classification":
                loss_fct = CrossEntropyLoss()
                loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))
            elif self.config.problem_type == "multi_label_classification":
                loss_fct = BCEWithLogitsLoss()
                loss = loss_fct(logits, labels)
        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return SequenceClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )


@add_start_docstrings(
    """
    CANINE Model with a multiple choice classification head on top (a linear layer on top of the pooled output and a
    softmax) e.g. for RocStories/SWAG tasks.
    """,
    CANINE_START_DOCSTRING,
)
class CanineForMultipleChoice(CaninePreTrainedModel):
    def __init__(self, config):
        super().__init__(config)

        self.canine = CanineModel(config)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)
        self.classifier = nn.Linear(config.hidden_size, 1)

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(CANINE_INPUTS_DOCSTRING.format("batch_size, num_choices, sequence_length"))
    @add_code_sample_docstrings(
        checkpoint=_CHECKPOINT_FOR_DOC,
        output_type=MultipleChoiceModelOutput,
        config_class=_CONFIG_FOR_DOC,
    )
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.FloatTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, MultipleChoiceModelOutput]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size,)`, *optional*):
            Labels for computing the multiple choice classification loss. Indices should be in `[0, ...,
            num_choices-1]` where `num_choices` is the size of the second dimension of the input tensors. (See
            `input_ids` above)
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
        num_choices = input_ids.shape[1] if input_ids is not None else inputs_embeds.shape[1]

        input_ids = input_ids.view(-1, input_ids.size(-1)) if input_ids is not None else None
        attention_mask = attention_mask.view(-1, attention_mask.size(-1)) if attention_mask is not None else None
        token_type_ids = token_type_ids.view(-1, token_type_ids.size(-1)) if token_type_ids is not None else None
        position_ids = position_ids.view(-1, position_ids.size(-1)) if position_ids is not None else None
        inputs_embeds = (
            inputs_embeds.view(-1, inputs_embeds.size(-2), inputs_embeds.size(-1))
            if inputs_embeds is not None
            else None
        )

        outputs = self.canine(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        pooled_output = outputs[1]

        pooled_output = self.dropout(pooled_output)
        logits = self.classifier(pooled_output)
        reshaped_logits = logits.view(-1, num_choices)

        loss = None
        if labels is not None:
            loss_fct = CrossEntropyLoss()
            loss = loss_fct(reshaped_logits, labels)

        if not return_dict:
            output = (reshaped_logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return MultipleChoiceModelOutput(
            loss=loss,
            logits=reshaped_logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )


@add_start_docstrings(
    """
    CANINE Model with a token classification head on top (a linear layer on top of the hidden-states output) e.g. for
    Named-Entity-Recognition (NER) tasks.
    """,
    CANINE_START_DOCSTRING,
)
class CanineForTokenClassification(CaninePreTrainedModel):
    def __init__(self, config):
        super().__init__(config)
        self.num_labels = config.num_labels

        self.canine = CanineModel(config)
        self.dropout = nn.Dropout(config.hidden_dropout_prob)
        self.classifier = nn.Linear(config.hidden_size, config.num_labels)

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(CANINE_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @replace_return_docstrings(output_type=TokenClassifierOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.FloatTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        labels: Optional[torch.LongTensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, TokenClassifierOutput]:
        r"""
        labels (`torch.LongTensor` of shape `(batch_size, sequence_length)`, *optional*):
            Labels for computing the token classification loss. Indices should be in `[0, ..., config.num_labels - 1]`.

        Returns:

        Example:

        ```python
        >>> from transformers import AutoTokenizer, CanineForTokenClassification
        >>> import torch

        >>> tokenizer = AutoTokenizer.from_pretrained("google/canine-s")
        >>> model = CanineForTokenClassification.from_pretrained("google/canine-s")

        >>> inputs = tokenizer(
        ...     "HuggingFace is a company based in Paris and New York", add_special_tokens=False, return_tensors="pt"
        ... )

        >>> with torch.no_grad():
        ...     logits = model(**inputs).logits

        >>> predicted_token_class_ids = logits.argmax(-1)

        >>> # Note that tokens are classified rather then input words which means that
        >>> # there might be more predicted token classes than words.
        >>> # Multiple token classes might account for the same word
        >>> predicted_tokens_classes = [model.config.id2label[t.item()] for t in predicted_token_class_ids[0]]
        >>> predicted_tokens_classes  # doctest: +SKIP
        ```

        ```python
        >>> labels = predicted_token_class_ids
        >>> loss = model(**inputs, labels=labels).loss
        >>> round(loss.item(), 2)  # doctest: +SKIP
        ```"""
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.canine(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        sequence_output = outputs[0]

        sequence_output = self.dropout(sequence_output)
        logits = self.classifier(sequence_output)

        loss = None
        if labels is not None:
            loss_fct = CrossEntropyLoss()
            loss = loss_fct(logits.view(-1, self.num_labels), labels.view(-1))

        if not return_dict:
            output = (logits,) + outputs[2:]
            return ((loss,) + output) if loss is not None else output

        return TokenClassifierOutput(
            loss=loss,
            logits=logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )


@add_start_docstrings(
    """
    CANINE Model with a span classification head on top for extractive question-answering tasks like SQuAD (a linear
    layers on top of the hidden-states output to compute `span start logits` and `span end logits`).
    """,
    CANINE_START_DOCSTRING,
)
class CanineForQuestionAnswering(CaninePreTrainedModel):
    def __init__(self, config):
        super().__init__(config)
        self.num_labels = config.num_labels

        self.canine = CanineModel(config)
        self.qa_outputs = nn.Linear(config.hidden_size, config.num_labels)

        # Initialize weights and apply final processing
        self.post_init()

    @add_start_docstrings_to_model_forward(CANINE_INPUTS_DOCSTRING.format("batch_size, sequence_length"))
    @add_code_sample_docstrings(
        checkpoint="Splend1dchan/canine-c-squad",
        output_type=QuestionAnsweringModelOutput,
        config_class=_CONFIG_FOR_DOC,
        expected_output="'nice puppet'",
        expected_loss=8.81,
    )
    def forward(
        self,
        input_ids: Optional[torch.LongTensor] = None,
        attention_mask: Optional[torch.FloatTensor] = None,
        token_type_ids: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        head_mask: Optional[torch.FloatTensor] = None,
        inputs_embeds: Optional[torch.FloatTensor] = None,
        start_positions: Optional[torch.LongTensor] = None,
        end_positions: Optional[torch.LongTensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, QuestionAnsweringModelOutput]:
        r"""
        start_positions (`torch.LongTensor` of shape `(batch_size,)`, *optional*):
            Labels for position (index) of the start of the labelled span for computing the token classification loss.
            Positions are clamped to the length of the sequence (`sequence_length`). Position outside of the sequence
            are not taken into account for computing the loss.
        end_positions (`torch.LongTensor` of shape `(batch_size,)`, *optional*):
            Labels for position (index) of the end of the labelled span for computing the token classification loss.
            Positions are clamped to the length of the sequence (`sequence_length`). Position outside of the sequence
            are not taken into account for computing the loss.
        """
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        outputs = self.canine(
            input_ids,
            attention_mask=attention_mask,
            token_type_ids=token_type_ids,
            position_ids=position_ids,
            head_mask=head_mask,
            inputs_embeds=inputs_embeds,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )

        sequence_output = outputs[0]

        logits = self.qa_outputs(sequence_output)
        start_logits, end_logits = logits.split(1, dim=-1)
        start_logits = start_logits.squeeze(-1)
        end_logits = end_logits.squeeze(-1)

        total_loss = None
        if start_positions is not None and end_positions is not None:
            # If we are on multi-GPU, split add a dimension
            if len(start_positions.size()) > 1:
                start_positions = start_positions.squeeze(-1)
            if len(end_positions.size()) > 1:
                end_positions = end_positions.squeeze(-1)
            # sometimes the start/end positions are outside our model inputs, we ignore these terms
            ignored_index = start_logits.size(1)
            start_positions.clamp_(0, ignored_index)
            end_positions.clamp_(0, ignored_index)

            loss_fct = CrossEntropyLoss(ignore_index=ignored_index)
            start_loss = loss_fct(start_logits, start_positions)
            end_loss = loss_fct(end_logits, end_positions)
            total_loss = (start_loss + end_loss) / 2

        if not return_dict:
            output = (start_logits, end_logits) + outputs[2:]
            return ((total_loss,) + output) if total_loss is not None else output

        return QuestionAnsweringModelOutput(
            loss=total_loss,
            start_logits=start_logits,
            end_logits=end_logits,
            hidden_states=outputs.hidden_states,
            attentions=outputs.attentions,
        )