peft/tuners/prompt_tuning/model.py

# Copyright 2023-present 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.

import math

import torch

from peft.utils.integrations import gather_params_ctx

from .config import PromptTuningInit


class PromptEmbedding(torch.nn.Module):
    """
    The model to encode virtual tokens into prompt embeddings.

    Args:
        config ([`PromptTuningConfig`]): The configuration of the prompt embedding.
        word_embeddings (`torch.nn.Module`): The word embeddings of the base transformer model.

    **Attributes**:
        - **embedding** (`torch.nn.Embedding`) -- The embedding layer of the prompt embedding.

    Example:

    ```py
    >>> from peft import PromptEmbedding, PromptTuningConfig

    >>> config = PromptTuningConfig(
    ...     peft_type="PROMPT_TUNING",
    ...     task_type="SEQ_2_SEQ_LM",
    ...     num_virtual_tokens=20,
    ...     token_dim=768,
    ...     num_transformer_submodules=1,
    ...     num_attention_heads=12,
    ...     num_layers=12,
    ...     prompt_tuning_init="TEXT",
    ...     prompt_tuning_init_text="Predict if sentiment of this review is positive, negative or neutral",
    ...     tokenizer_name_or_path="t5-base",
    ... )

    >>> # t5_model.shared is the word embeddings of the base model
    >>> prompt_embedding = PromptEmbedding(config, t5_model.shared)
    ```

    Input Shape: (`batch_size`, `total_virtual_tokens`)

    Output Shape: (`batch_size`, `total_virtual_tokens`, `token_dim`)
    """

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

        total_virtual_tokens = config.num_virtual_tokens * config.num_transformer_submodules
        self.embedding = torch.nn.Embedding(total_virtual_tokens, config.token_dim)
        if config.prompt_tuning_init == PromptTuningInit.TEXT and not config.inference_mode:
            from transformers import AutoTokenizer

            tokenizer_kwargs = config.tokenizer_kwargs or {}
            tokenizer = AutoTokenizer.from_pretrained(config.tokenizer_name_or_path, **tokenizer_kwargs)
            init_text = config.prompt_tuning_init_text
            init_token_ids = tokenizer(init_text)["input_ids"]
            # Trim or iterate until num_text_tokens matches total_virtual_tokens
            num_text_tokens = len(init_token_ids)
            if num_text_tokens > total_virtual_tokens:
                init_token_ids = init_token_ids[:total_virtual_tokens]
            elif num_text_tokens < total_virtual_tokens:
                num_reps = math.ceil(total_virtual_tokens / num_text_tokens)
                init_token_ids = init_token_ids * num_reps
            init_token_ids = init_token_ids[:total_virtual_tokens]
            init_token_ids = torch.LongTensor(init_token_ids).to(word_embeddings.weight.device)
            with gather_params_ctx(word_embeddings.parameters()):
                word_embedding_weights = word_embeddings(init_token_ids).detach().clone()
            word_embedding_weights = word_embedding_weights.to(torch.float32)
            self.embedding.weight = torch.nn.Parameter(word_embedding_weights)

    def forward(self, indices):
        # Just get embeddings
        prompt_embeddings = self.embedding(indices)
        return prompt_embeddings