verl/workers/reward_model/base.py

# Copyright 2024 Bytedance Ltd. and/or its affiliates
#
# 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
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# distributed under the License is distributed on an "AS IS" BASIS,
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"""
The base class for reward model
"""

from abc import ABC, abstractmethod

from verl import DataProto


class BasePPORewardModel(ABC):
    def __init__(self, config):
        self.config = config

    @abstractmethod
    def compute_reward(self, data: DataProto) -> DataProto:
        """Computing reward given input_ids. The transformers should output a tensor with shape
           [batch_size, sequence_length], and the value at [EOS] mask should be gathered.

        Args:
            data: must contain keys "input_ids", "attention_mask" and "position_ids".
                - input_ids: [batch_size, sequence_length]
                - attention_mask: [batch_size, sequence_length]
                - position_ids: [batch_size, sequence_length]

        Returns: a data pass protocol containing "reward". Only the [EOS] position contains the reward.
            Other position should have zero reward. Note that this may change in the future if we use
            dense reward. So, we leave the interface for general case.
            - reward: [batch_size, sequence_length].

        """
        pass