shunk031-python-transformers-convert

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SKILL.md
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SKILL.md
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Hugging Face Transformers Model Conversion

Hugging Face Transformers 模型转换

Convert custom PyTorch models to Hugging Face Transformers format while maintaining exact compatibility with the original implementation.
将自定义 PyTorch 模型转换为 Hugging Face Transformers 格式,同时保持与原始实现的精确兼容性。

Overview

概述

This skill provides a systematic workflow for transformers conversion:
  • Extract hardcoded values into PretrainedConfig
  • Create PreTrainedModel wrapper
  • Build ImageProcessor/Tokenizer
  • Test equivalence thoroughly
  • Prepare for Hub upload
Important: Use validation mode (parallel implementations) first to verify equivalence, then replace the original.
此 skill 提供用于 transformers 转换的系统化工作流:
  • 将硬编码值提取到 PretrainedConfig
  • 创建 PreTrainedModel 包装器
  • 构建 ImageProcessor/Tokenizer
  • 全面测试等价性
  • 准备上传至 Hub
重要:先使用验证模式(并行实现)验证等价性,然后替换原始实现。

Conversion Workflow

转换工作流

Step 1: Analyze the Custom Model

第 1 步:分析自定义模型

Ask the user to specify:
  • Path to the custom model implementation
  • Model type (vision, text, multimodal)
  • Task (classification, segmentation, generation, etc.)
  • Validation mode or replacement mode
Then identify:
  • Model architecture and components
  • Input/output formats
  • Key hyperparameters and hardcoded values
  • Pretrained weights location
  • Preprocessing pipeline
  • Custom layers or modules
要求用户指定:
  • 自定义模型实现的路径
  • 模型类型(视觉、文本、多模态)
  • 任务(分类、分割、生成等)
  • 验证模式或替换模式
然后确定:
  • 模型架构和组件
  • 输入/输出格式
  • 关键超参数和硬编码值
  • 预训练权重位置
  • 预处理流水线
  • 自定义层或模块

Step 2: Create PretrainedConfig Class

第 2 步:创建 PretrainedConfig 类

Key principle: Extract ALL hardcoded values from the model as configurable parameters.
Template:
python
from transformers import PretrainedConfig
from typing import List, Optional

class {ModelName}Config(PretrainedConfig):
    model_type = "{model_name}"

    def __init__(
        self,
        # Core architecture parameters
        hidden_dim: int = 128,
        num_layers: int = 4,

        # Input/output parameters
        image_size: int = 1024,
        num_channels: int = 3,
        num_labels: int = 1,

        # Component-specific parameters (extract from original)
        component_param: List[int] | None = None,

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

        self.hidden_dim = hidden_dim
        self.num_layers = num_layers
        self.image_size = image_size
        self.num_channels = num_channels
        self.num_labels = num_labels

        # Use default if not specified
        self.component_param = (
            component_param if component_param is not None else [1, 2, 4]
        )
Critical: Ensure default values match what the pretrained weights expect!
核心原则:将模型中的所有硬编码值提取为可配置参数。
模板:
python
from transformers import PretrainedConfig
from typing import List, Optional

class {ModelName}Config(PretrainedConfig):
    model_type = "{model_name}"

    def __init__(
        self,
        # Core architecture parameters
        hidden_dim: int = 128,
        num_layers: int = 4,

        # Input/output parameters
        image_size: int = 1024,
        num_channels: int = 3,
        num_labels: int = 1,

        # Component-specific parameters (extract from original)
        component_param: List[int] | None = None,

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

        self.hidden_dim = hidden_dim
        self.num_layers = num_layers
        self.image_size = image_size
        self.num_channels = num_channels
        self.num_labels = num_labels

        # Use default if not specified
        self.component_param = (
            component_param if component_param is not None else [1, 2, 4]
        )
关键:确保默认值与预训练权重的预期一致!

Step 3: Create PreTrainedModel Class

第 3 步:创建 PreTrainedModel 类

Template:
python
from transformers import PreTrainedModel
from transformers.modeling_outputs import SemanticSegmenterOutput

class {ModelName}ForTask(PreTrainedModel):
    config_class = {ModelName}Config

    def __init__(self, config: {ModelName}Config):
        super().__init__(config)
        self.config = config

        # Initialize layers using config parameters (no hardcoded values!)
        self.encoder = Encoder(
            hidden_dim=config.hidden_dim,
            num_layers=config.num_layers,
        )

    def forward(
        self,
        pixel_values: torch.FloatTensor,
        labels: Optional[torch.LongTensor] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, SemanticSegmenterOutput]:
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        # Forward pass
        logits = self.encoder(pixel_values)

        # Calculate loss if needed
        loss = None
        if labels is not None:
            # Compute loss
            pass

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

        return SemanticSegmenterOutput(
            loss=loss,
            logits=logits,
            hidden_states=None,
            attentions=None,
        )
模板:
python
from transformers import PreTrainedModel
from transformers.modeling_outputs import SemanticSegmenterOutput

class {ModelName}ForTask(PreTrainedModel):
    config_class = {ModelName}Config

    def __init__(self, config: {ModelName}Config):
        super().__init__(config)
        self.config = config

        # Initialize layers using config parameters (no hardcoded values!)
        self.encoder = Encoder(
            hidden_dim=config.hidden_dim,
            num_layers=config.num_layers,
        )

    def forward(
        self,
        pixel_values: torch.FloatTensor,
        labels: Optional[torch.LongTensor] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, SemanticSegmenterOutput]:
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        # Forward pass
        logits = self.encoder(pixel_values)

        # Calculate loss if needed
        loss = None
        if labels is not None:
            # Compute loss
            pass

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

        return SemanticSegmenterOutput(
            loss=loss,
            logits=logits,
            hidden_states=None,
            attentions=None,
        )

Step 4: Create ImageProcessor/Tokenizer

第 4 步:创建 ImageProcessor/Tokenizer

For vision models - Create ImageProcessor:
python
from transformers import BaseImageProcessor

class {ModelName}ImageProcessor(BaseImageProcessor):
    model_input_names = ["pixel_values"]

    def __init__(
        self,
        size: int = 1024,
        resample: str = "bilinear",
        do_normalize: bool = True,
        image_mean: List[float] | None = None,
        image_std: List[float] | None = None,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.size = size
        self.resample = resample
        self.do_normalize = do_normalize
        self.image_mean = image_mean if image_mean is not None else [0.485, 0.456, 0.406]
        self.image_std = image_std if image_std is not None else [0.229, 0.224, 0.225]

    def preprocess(
        self,
        images: ImageInput,
        return_tensors: Optional[Union[str, TensorType]] = None,
        **kwargs,
    ) -> BatchFeature:
        # Implement preprocessing matching original
        # Return BatchFeature with pixel_values
For text models - Create tokenizer configuration.
对于视觉模型——创建 ImageProcessor:
python
from transformers import BaseImageProcessor

class {ModelName}ImageProcessor(BaseImageProcessor):
    model_input_names = ["pixel_values"]

    def __init__(
        self,
        size: int = 1024,
        resample: str = "bilinear",
        do_normalize: bool = True,
        image_mean: List[float] | None = None,
        image_std: List[float] | None = None,
        **kwargs,
    ):
        super().__init__(**kwargs)
        self.size = size
        self.resample = resample
        self.do_normalize = do_normalize
        self.image_mean = image_mean if image_mean is not None else [0.485, 0.456, 0.406]
        self.image_std = image_std if image_std is not None else [0.229, 0.224, 0.225]

    def preprocess(
        self,
        images: ImageInput,
        return_tensors: Optional[Union[str, TensorType]] = None,
        **kwargs,
    ) -> BatchFeature:
        # Implement preprocessing matching original
        # Return BatchFeature with pixel_values
对于文本模型——创建 tokenizer 配置。

Step 5: Create Compatibility Tests

第 5 步:创建兼容性测试

Critical: Always use the SAME preprocessed tensor for both models when comparing outputs.
python
import pytest
import torch

def test_preprocessing_matches():
    """Test that preprocessing is equivalent."""
    old_tensor = old_preprocessing(image)
    new_tensor = processor(image, return_tensors="pt")["pixel_values"][0]
    assert torch.allclose(old_tensor, new_tensor, atol=1e-6)

def test_single_image_output_matches():
    """Test that model outputs match."""
    # Load models
    old_model = OldModel()
    new_model = NewModel(NewConfig())
    new_model.load_state_dict(old_model.state_dict())

    # Prepare SAME input
    preprocessed = preprocess(image)

    with torch.no_grad():
        old_output = old_model(preprocessed)
        new_output = new_model(pixel_values=preprocessed)

    # Use 0.5% tolerance for numerical differences
    assert torch.allclose(old_output, new_output.logits, atol=5e-3, rtol=1e-2)

def test_batch_output_matches():
    """Test batch processing."""
    # Test with batch of images

def test_state_dict_compatible():
    """Test that weights can be loaded."""
    new_model.load_state_dict(old_model.state_dict())
关键:比较两个模型的输出时,始终使用相同的预处理张量。
python
import pytest
import torch

def test_preprocessing_matches():
    """Test that preprocessing is equivalent."""
    old_tensor = old_preprocessing(image)
    new_tensor = processor(image, return_tensors="pt")["pixel_values"][0]
    assert torch.allclose(old_tensor, new_tensor, atol=1e-6)

def test_single_image_output_matches():
    """Test that model outputs match."""
    # Load models
    old_model = OldModel()
    new_model = NewModel(NewConfig())
    new_model.load_state_dict(old_model.state_dict())

    # Prepare SAME input
    preprocessed = preprocess(image)

    with torch.no_grad():
        old_output = old_model(preprocessed)
        new_output = new_model(pixel_values=preprocessed)

    # Use 0.5% tolerance for numerical differences
    assert torch.allclose(old_output, new_output.logits, atol=5e-3, rtol=1e-2)

def test_batch_output_matches():
    """Test batch processing."""
    # Test with batch of images

def test_state_dict_compatible():
    """Test that weights can be loaded."""
    new_model.load_state_dict(old_model.state_dict())

Step 6: Create MODEL_CARD.md

第 6 步:创建 MODEL_CARD.md

Generate comprehensive model card following Hugging Face standards. Include:
  • Model description
  • Usage examples
  • Training details
  • Evaluation metrics
  • Citation information
See Hugging Face model card documentation for template.
按照 Hugging Face 标准生成全面的模型卡。包含:
  • 模型描述
  • 使用示例
  • 训练细节
  • 评估指标
  • 引用信息
有关模板,请参阅 Hugging Face 模型卡文档。

Step 7: Create Hub Push Script

第 7 步:创建 Hub 推送脚本

Critical: Register classes with
register_for_auto_class()
before pushing.
python
#!/usr/bin/env python3
from huggingface_hub import HfApi
from {module}.transformers import {ModelName}Config, {ModelName}ForTask, {ModelName}ImageProcessor

def main():
    # CRITICAL: Register for Auto* support
    {ModelName}Config.register_for_auto_class()
    {ModelName}ForTask.register_for_auto_class("AutoModel")
    {ModelName}ImageProcessor.register_for_auto_class("AutoImageProcessor")

    # Load original model
    original_model = OriginalModel()

    # Create transformers-compatible model
    config = {ModelName}Config()
    model = {ModelName}ForTask(config)
    model.load_state_dict(original_model.state_dict())

    # Save and push
    model.save_pretrained(local_dir)
    config.save_pretrained(local_dir)
    processor = {ModelName}ImageProcessor()
    processor.save_pretrained(local_dir)

    api = HfApi(token=token)
    api.create_repo(repo_id=repo_id, exist_ok=True)
    api.upload_folder(repo_id=repo_id, folder_path=local_dir)
关键:推送前,使用
register_for_auto_class()
注册类。
python
#!/usr/bin/env python3
from huggingface_hub import HfApi
from {module}.transformers import {ModelName}Config, {ModelName}ForTask, {ModelName}ImageProcessor

def main():
    # CRITICAL: Register for Auto* support
    {ModelName}Config.register_for_auto_class()
    {ModelName}ForTask.register_for_auto_class("AutoModel")
    {ModelName}ImageProcessor.register_for_auto_class("AutoImageProcessor")

    # Load original model
    original_model = OriginalModel()

    # Create transformers-compatible model
    config = {ModelName}Config()
    model = {ModelName}ForTask(config)
    model.load_state_dict(original_model.state_dict())

    # Save and push
    model.save_pretrained(local_dir)
    config.save_pretrained(local_dir)
    processor = {ModelName}ImageProcessor()
    processor.save_pretrained(local_dir)

    api = HfApi(token=token)
    api.create_repo(repo_id=repo_id, exist_ok=True)
    api.upload_folder(repo_id=repo_id, folder_path=local_dir)

Implementation Strategy

实现策略

Validation Mode (Recommended First)

验证模式(建议首先使用)

Create parallel implementations:
{project}/
├── {module}/
│   ├── original_model.py           # Existing
│   └── transformers/               # NEW - for validation
│       ├── __init__.py
│       ├── configuration_{model}.py
│       ├── modeling_{model}.py
│       └── processing_{model}.py
└── tests/
    └── test_transformers_compatibility.py
Workflow:
  1. Create transformers/ package alongside original
  2. Run compatibility tests
  3. Debug any discrepancies
  4. Once tests pass → proceed to replacement
创建并行实现:
{project}/
├── {module}/
│   ├── original_model.py           # Existing
│   └── transformers/               # NEW - for validation
│       ├── __init__.py
│       ├── configuration_{model}.py
│       ├── modeling_{model}.py
│       └── processing_{model}.py
└── tests/
    └── test_transformers_compatibility.py
工作流:
  1. 在原始实现旁创建 transformers/ 包
  2. 运行兼容性测试
  3. 调试任何差异
  4. 测试通过后 → 继续进行替换

Replacement Mode (After Validation)

替换模式(验证后)

Once equivalence is verified:
{project}/
└── {module}/
    ├── configuration_{model}.py    # Replaces original
    ├── modeling_{model}.py
    └── processing_{model}.py
Workflow:
  1. Remove or archive original implementation
  2. Move transformers/* files up one level
  3. Update all imports
  4. Update tests
  5. Update documentation
确认等价性后:
{project}/
└── {module}/
    ├── configuration_{model}.py    # Replaces original
    ├── modeling_{model}.py
    └── processing_{model}.py
工作流:
  1. 移除或归档原始实现
  2. 将 transformers/* 文件上移一层
  3. 更新所有导入
  4. 更新测试
  5. 更新文档

Common Issues

常见问题

For detailed troubleshooting, see references/common-pitfalls.md.
Quick reference:
  • Hardcoded values: Extract to config with matching defaults
  • Preprocessing mismatches: Use exact same pipeline and parameters
  • State dict keys: Keep layer names matching original
  • Test tolerance: Use 0.5% tolerance (5e-3) for numerical differences
  • Device handling: Use
    self.device
    from PreTrainedModel
  • Image size order:
    post_process_semantic_segmentation()
    expects
    (width, height)
有关详细故障排查,请参阅 references/common-pitfalls.md。
快速参考:
  • 硬编码值:提取到 config,并确保默认值匹配
  • 预处理不匹配:使用完全相同的流水线和参数
  • State dict 键:保持层名称与原始实现一致
  • 测试容差:数值差异使用 0.5% 容差(5e-3)
  • 设备处理:使用 PreTrainedModel 中的
    self.device
  • 图像尺寸顺序:
    post_process_semantic_segmentation()
    期望
    (width, height)

Debugging Strategy

调试策略

If outputs don't match:
  1. Check preprocessing produces identical tensors
  2. Check state dict loaded correctly
  3. Step-by-step comparison of each layer
  4. Check device placement
  5. Check determinism with torch.manual_seed
See references/common-pitfalls.md for detailed debugging steps.
如果输出不匹配:
  1. 检查预处理是否生成完全相同的张量
  2. 检查 state dict 是否正确加载
  3. 逐步比较每一层
  4. 检查设备放置
  5. 使用 torch.manual_seed 检查确定性
有关详细的调试步骤,请参阅 references/common-pitfalls.md。

Project Learnings

项目经验

After completing a conversion, add learnings to references/learnings.md.
This accumulates knowledge from each project to avoid repeating mistakes.
完成转换后,将经验添加到 references/learnings.md。
这会累积每个项目的知识,避免重复犯错。

Checklist

检查清单

  • Step 1: Model analyzed
    • Architecture identified
    • Hyperparameters extracted
    • Preprocessing understood
  • Step 2: Config class created
    • All hardcoded values moved to config
    • Defaults match pretrained weights
    • Type hints added
  • Step 3: Model class created
    • Inherits from PreTrainedModel
    • Uses only config parameters
    • Forward signature matches conventions
  • Step 4: Processor created
    • Preprocessing matches original
    • Returns appropriate format
  • Step 5: Tests created
    • Preprocessing test passes
    • Single image test passes
    • Batch test passes
    • State dict test passes
  • Step 6: MODEL_CARD.md created
    • All sections filled
    • Usage examples tested
    • Citations included
  • Step 7: Push script created
    • register_for_auto_class() called
    • Script tested locally
    • Successfully pushed to Hub
  • Cleanup (if doing replacement)
    • Original implementation removed/archived
    • Imports updated
    • Documentation updated
  • 第 1 步:模型已分析
    • 已确定架构
    • 已提取超参数
    • 已理解预处理流程
  • 第 2 步:已创建 Config 类
    • 所有硬编码值均已移至 config
    • 默认值与预训练权重匹配
    • 已添加类型提示
  • 第 3 步:已创建 Model 类
    • 继承自 PreTrainedModel
    • 仅使用 config 参数
    • forward 签名符合约定
  • 第 4 步:已创建 Processor
    • 预处理与原始实现一致
    • 返回适当的格式
  • 第 5 步:已创建测试
    • 预处理测试通过
    • 单张图像测试通过
    • 批量测试通过
    • State dict 测试通过
  • 第 6 步:已创建 MODEL_CARD.md
    • 所有章节均已填写
    • 使用示例已测试
    • 已包含引用
  • 第 7 步:已创建推送脚本
    • 已调用 register_for_auto_class()
    • 脚本已在本地测试
    • 已成功推送至 Hub
  • 清理(如果执行替换)
    • 原始实现已移除或归档
    • 导入已更新
    • 文档已更新