#
Integrate any ML framework with the Hub

The Hugging Face Hub makes hosting and sharing models with the community easy. It supports dozens of libraries in the Open Source ecosystem. We are always working on expanding this support to push collaborative Machine Learning forward. The `huggingface_hub` library plays a key role in this process, allowing any Python script to easily push and load files.

There are four main ways to integrate a library with the Hub:

1. Push to Hub: implement a method to upload a model to the Hub. This includes the model weights, as well as the model card and any other relevant information or data necessary to run the model (for example, training logs). This method is often called `push_to_hub()`.
2. Download from Hub: implement a method to load a model from the Hub. The method should download the model configuration/weights and load the model. This method is often called `from_pretrained` or `load_from_hub()`.
3. Inference API: use our servers to run inference on models supported by your library for free.
4. Widgets: display a widget on the landing page of your models on the Hub. It allows users to quickly try a model from the browser.

In this guide, we will focus on the first two topics. We will present the two main approaches you can use to integrate a library, with their advantages and drawbacks. Everything is summarized at the end of the guide to help you choose between the two. Please keep in mind that these are only guidelines that you are free to adapt to you requirements.

If you are interested in Inference and Widgets, you can follow this guide. In both cases, you can reach out to us if you are integrating a library with the Hub and want to be listed in our docs.

##
A flexible approach: helpers

The first approach to integrate a library to the Hub is to actually implement the `push_to_hub` and `from_pretrained` methods by yourself. This gives you full flexibility on which files you need to upload/download and how to handle inputs specific to your framework. You can refer to the two upload files and download files guides to learn more about how to do that. This is, for example how the FastAI integration is implemented (see push_to_hub_fastai() and from_pretrained_fastai()).

Implementation can differ between libraries, but the workflow is often similar.

###
from_pretrained

This is how a `from_pretrained` method usually look like:

    def from_pretrained(model_id: str) -> MyModelClass:
       # Download model from Hub
       cached_model = hf_hub_download(
          repo_id=repo_id,
          filename="model.pkl",
          library_name="fastai",
          library_version=get_fastai_version(),
       )

       # Load model
        return load_model(cached_model)

###
push_to_hub

The `push_to_hub` method often requires a bit more complexity to handle repo creation, generate the model card and save weights. A common approach is to save all of these files in a temporary folder, upload it and then delete it.

    def push_to_hub(model: MyModelClass, repo_name: str) -> None:
       api = HfApi()

       # Create repo if not existing yet and get the associated repo_id
       repo_id = api.create_repo(repo_name, exist_ok=True)

       # Save all files in a temporary directory and push them in a single commit
       with TemporaryDirectory() as tmpdir:
          tmpdir = Path(tmpdir)

          # Save weights
          save_model(model, tmpdir / "model.safetensors")

          # Generate model card
          card = generate_model_card(model)
          (tmpdir / "README.md").write_text(card)

          # Save logs
          # Save figures
          # Save evaluation metrics
          # ...

          # Push to hub
          return api.upload_folder(repo_id=repo_id, folder_path=tmpdir)

This is of course only an example. If you are interested in more complex manipulations (delete remote files, upload weights on the fly, persist weights locally, etc.) please refer to the upload files guide.

###
Limitations

While being flexible, this approach has some drawbacks, especially in terms of maintenance. Hugging Face users are often used to additional features when working with `huggingface_hub`. For example, when loading files from the Hub, it is common to offer parameters like:

- `token`: to download from a private repo
- `revision`: to download from a specific branch
- `cache_dir`: to cache files in a specific directory
- `force_download`/`resume_download`/`local_files_only`: to reuse the cache or not
- `api_endpoint`/`proxies`: configure HTTP session

When pushing models, similar parameters are supported:

- `commit_message`: custom commit message
- `private`: create a private repo if missing
- `create_pr`: create a PR instead of pushing to `main`
- `branch`: push to a branch instead of the `main` branch
- `allow_patterns`/`ignore_patterns`: filter which files to upload
- `token`
- `api_endpoint`
- …

All of these parameters can be added to the implementations we saw above and passed to the `huggingface_hub` methods. However, if a parameter changes or a new feature is added, you will need to update your package. Supporting those parameters also means more documentation to maintain on your side. To see how to mitigate these limitations, let’s jump to our next section class inheritance.

##
A more complex approach: class inheritance

As we saw above, there are two main methods to include in your library to integrate it with the Hub: upload files (`push_to_hub`) and download files (`from_pretrained`). You can implement those methods by yourself but it comes with caveats. To tackle this, `huggingface_hub` provides a tool that uses class inheritance. Let’s see how it works!

In a lot of cases, a library already implements its model using a Python class. The class contains the properties of the model and methods to load, run, train, and evaluate it. Our approach is to extend this class to include upload and download features using mixins. A Mixin is a class that is meant to extend an existing class with a set of specific features using multiple inheritance. `huggingface_hub` provides its own mixin, the ModelHubMixin. The key here is to understand its behavior and how to customize it.

The ModelHubMixin class implements 3 public methods (`push_to_hub`, `save_pretrained` and `from_pretrained`). Those are the methods that your users will call to load/save models with your library. ModelHubMixin also defines 2 private methods (`_save_pretrained` and `_from_pretrained`). Those are the ones you must implement. So to integrate your library, you should:

1. Make your Model class inherit from ModelHubMixin.
2. Implement the private methods:
   - _save_pretrained(): method taking as input a path to a directory and saving the model to it. You must write all the logic to dump your model in this method: model card, model weights, configuration files, training logs, and figures. Any relevant information for this model must be handled by this method. Model Cards are particularly important to describe your model. Check out our implementation guide for more details.
   - _from_pretrained(): class method taking as input a `model_id` and returning an instantiated model. The method must download the relevant files and load them.
3. You are done!

The advantage of using ModelHubMixin is that once you take care of the serialization/loading of the files, you are ready to go. You don’t need to worry about stuff like repo creation, commits, PRs, or revisions. All of this is handled by the mixin and is available to your users. The Mixin also ensures that public methods are well documented and type annotated.

###
A concrete example: PyTorch

A good example of what we saw above is PyTorchModelHubMixin, our integration for the PyTorch framework. This is a ready-to-use integration.

####
How to use it?

Here is how any user can load/save a PyTorch model from/to the Hub:

    >>> import torch
    >>> import torch.nn as nn
    >>> from huggingface_hub import PyTorchModelHubMixin

    # 1. Define your Pytorch model exactly the same way you are used to
    >>> class MyModel(nn.Module, PyTorchModelHubMixin): # multiple inheritance
    ...     def __init__(self):
    ...         super().__init__()
    ...         self.param = nn.Parameter(torch.rand(3, 4))
    ...         self.linear = nn.Linear(4, 5)

    ...     def forward(self, x):
    ...         return self.linear(x + self.param)
    >>> model = MyModel()

    # 2. (optional) Save model to local directory
    >>> model.save_pretrained("path/to/my-awesome-model")

    # 3. Push model weights to the Hub
    >>> model.push_to_hub("my-awesome-model")

    # 4. Initialize model from the Hub
    >>> model = MyModel.from_pretrained("username/my-awesome-model")

####
Implementation

The implementation is actually very straightforward, and the full implementation can be found here.

1. First, inherit your class from `ModelHubMixin`:

    from huggingface_hub import ModelHubMixin

    class PyTorchModelHubMixin(ModelHubMixin):
       (...)

2. Implement the `_save_pretrained` method:

    from huggingface_hub import ModelCard, ModelCardData

    class PyTorchModelHubMixin(ModelHubMixin):
       (...)

       def _save_pretrained(self, save_directory: Path):
          """Generate Model Card and save weights from a Pytorch model to a local directory."""
          model_card = ModelCard.from_template(
             card_data=ModelCardData(
                license='mit',
                library_name="pytorch",
                ...
             ),
             model_summary=...,
             model_type=...,
             ...
          )
          (save_directory / "README.md").write_text(str(model))
          torch.save(obj=self.module.state_dict(), f=save_directory / "pytorch_model.bin")

3. Implement the `_from_pretrained` method:

    class PyTorchModelHubMixin(ModelHubMixin):
       (...)

       @classmethod # Must be a classmethod!
       def _from_pretrained(
          cls,
          *,
          model_id: str,
          revision: str,
          cache_dir: str,
          force_download: bool,
          proxies: Optional[Dict],
          resume_download: bool,
          local_files_only: bool,
          token: Union[str, bool, None],
          map_location: str = "cpu", # additional argument
          strict: bool = False, # additional argument
          **model_kwargs,
       ):
          """Load Pytorch pretrained weights and return the loaded model."""
          if os.path.isdir(model_id): # Can either be a local directory
             print("Loading weights from local directory")
             model_file = os.path.join(model_id, "pytorch_model.bin")
          else: # Or a model on the Hub
             model_file = hf_hub_download( # Download from the hub, passing same input args
                repo_id=model_id,
                filename="pytorch_model.bin",
                revision=revision,
                cache_dir=cache_dir,
                force_download=force_download,
                proxies=proxies,
                resume_download=resume_download,
                token=token,
                local_files_only=local_files_only,
             )

          # Load model and return - custom logic depending on your framework
          model = cls(**model_kwargs)
          state_dict = torch.load(model_file, map_location=torch.device(map_location))
          model.load_state_dict(state_dict, strict=strict)
          model.eval()
          return model

And that’s it! Your library now enables users to upload and download files to and from the Hub.

##
Quick comparison

Let’s quickly sum up the two approaches we saw with their advantages and drawbacks. The table below is only indicative. Your framework might have some specificities that you need to address. This guide is only here to give guidelines and ideas on how to handle integration. In any case, feel free to contact us if you have any questions!

Integration | Using helpers | Using ModelHubMixin
--- | --- | ---
User experience | `model = load_from_hub(...)` `push_to_hub(model, ...)` | `model = MyModel.from_pretrained(...)` `model.push_to_hub(...)`
Flexibility | Very flexible. You fully control the implementation. | Less flexible. Your framework must have a model class.
Maintenance | More maintenance to add support for configuration, and new features. Might also require fixing issues reported by users. | Less maintenance as most of the interactions with the Hub are implemented in `huggingface_hub`.
Documentation / Type annotation | To be written manually. | Partially handled by `huggingface_hub`.