Create custom Inference Handler

Hugging Face Endpoints supports all of the Transformers and Sentence-Transformers tasks and can support custom tasks, including custom pre- & post-processing. The customization can be done through a handler.py file in your model repository on the Hugging Face Hub.

The handler.py needs to implement the EndpointHandler class with a __init__ and a __call__ method.

If you want to use custom dependencies, e.g. optimum, the dependencies must be listed in a requirements.txt as described above in “add custom dependencies.”

Custom Handler Examples

There are already several public examples on the Hugging Face Hub where you can take insipiration or directly use them. The repositories are tagged with endpoints-template and can be found under this link.

Included examples are for:

Tutorial

Before creating a Custom Handler, you need a Hugging Face Model repository with your model weights and an Access Token with WRITE access to the repository. To find, create and manage Access Tokens, click here.

If you want to write a Custom Handler for an existing model from the community, you can use the repo_duplicator to create a repository fork.

The code can also be found in this Notebook.

You can also search for already existing Custom Handlers here: https://huggingface.co/models?other=endpoints-template

1. Set up Development Environment

The easiest way to develop our custom handler is to set up a local development environment, to implement, test, and iterate there, and then deploy it as an Inference Endpoint. The first step is to install all required development dependencies. needed to create the custom handler, not needed for inference

# install git-lfs to interact with the repository
sudo apt-get update
sudo apt-get install git-lfs
# install transformers (not needed since it is installed by default in the container)
pip install transformers[sklearn,sentencepiece,audio,vision]

After we have installed our libraries we will clone our repository to our development environment.

We will use philschmid/distilbert-base-uncased-emotion during the tutorial.

git lfs install
git clone https://huggingface.co/philschmid/distilbert-base-uncased-emotion

To be able to push our model repo later you need to login into our HF account. This can be done by using the huggingface-cli.

Note: Make sure to configure git config as well.

# setup cli with token
huggingface-cli login
git config --global credential.helper store

2. Create EndpointHandler

After we have set up our environment, we can start creating your custom handler. The custom handler is a Python class (EndpointHandler) inside a handler.py file in our repository. The EndpointHandler needs to implement an __init__ and a __call__ method.

The __init__ method will be called when starting the Endpoint and will receive 1 argument, a string with the path to your model weights. This allows you to load your model correctly.
The __call__ method will be called on every request and receive a dictionary with your request body as a python dictionary. It will always contain the inputs key.

The first step is to create our handler.py in the local clone of our repository.

!cd distilbert-base-uncased-emotion && touch handler.py

In there, you define your EndpointHandler class with the __init__ and __call__ method.

from typing import Dict, List, Any

class EndpointHandler():
    def __init__(self, path=""):
        # Preload all the elements you are going to need at inference.
        # pseudo:
        # self.model= load_model(path)

    def __call__(self, data: Dict[str, Any]) -> List[Dict[str, Any]]:
        """
       data args:
            inputs (:obj: `str` | `PIL.Image` | `np.array`)
            kwargs
      Return:
            A :obj:`list` | `dict`: will be serialized and returned
        """

        # pseudo
        # self.model(input)

3. Customize EndpointHandler

Now, you can add all of the custom logic you want to use during initialization or inference to your Custom Endpoint. You can already find multiple Custom Handler on the Hub if you need some inspiration. In our example, we will add a custom condition based on additional payload information.

The model we are using in the tutorial is fine-tuned to detect emotions. We will add an additional payload field for the date, and will use an external package to check if it is a holiday, to add a condition so that when the input date is a holiday, the model returns “happy” - since everyone is happy when there are holidays 🌴🎉😆

First, we need to create a new requirements.txt and add our holiday detection package and make sure we have it installed in our development environment as well.

!echo "holidays" >> requirements.txt
!pip install -r requirements.txt

Next, we have to adjust our handler.py and EndpointHandler to match our condition.

from typing import Dict, List, Any
from transformers import pipeline
import holidays

class EndpointHandler():
    def __init__(self, path=""):
        self.pipeline = pipeline("text-classification",model=path)
        self.holidays = holidays.US()

    def __call__(self, data: Dict[str, Any]) -> List[Dict[str, Any]]:
        """
       data args:
            inputs (:obj: `str`)
            date (:obj: `str`)
      Return:
            A :obj:`list` | `dict`: will be serialized and returned
        """
        # get inputs
        inputs = data.pop("inputs",data)
        date = data.pop("date", None)

        # check if date exists and if it is a holiday
        if date is not None and date in self.holidays:
          return [{"label": "happy", "score": 1}]


        # run normal prediction
        prediction = self.pipeline(inputs)
        return prediction

4. Test EndpointHandler

To test our EndpointHandler, we can simplify import, initialize and test it. Therefore we only need to prepare a sample payload.

from handler import EndpointHandler

# init handler
my_handler = EndpointHandler(path=".")

# prepare sample payload
non_holiday_payload = {"inputs": "I am quite excited how this will turn out", "date": "2022-08-08"}
holiday_payload = {"inputs": "Today is a though day", "date": "2022-07-04"}

# test the handler
non_holiday_pred=my_handler(non_holiday_payload)
holiday_payload=my_handler(holiday_payload)

# show results
print("non_holiday_pred", non_holiday_pred)
print("holiday_payload", holiday_payload)

# non_holiday_pred [{'label': 'joy', 'score': 0.9985942244529724}]
# holiday_payload [{'label': 'happy', 'score': 1}]

It works!!!! 🎉

Note: If you are using a notebook you might have to restart your kernel when you make changes to the handler.py since it is not automatically re-imported.

5. Push the Custom Handler to your repository

After you have successfully tested your handler locally, you can push it to your repository by simply using basic git commands.

# add all our new files
!git add *
# commit our files
!git commit -m "add custom handler"
# push the files to the hub
!git push

Now, you should see your handler.py and requirements.txt in your repository in the “Files and version” tab.

6. Deploy your Custom Handler as an Inference Endpoint

The last step is to deploy your Custom Handler as an Inference Endpoint. You can deploy your Custom Handler like you would a regular Inference Endpoint. Add your repository, select your cloud and region, your instance and security setting, and deploy.

When creating your Endpoint, the Inference Endpoint Service will check for an available and valid handler.py, and will use it for serving requests no matter which “Task” you select.

Note: In your Inference Endpoints dashboard, the Task for this Endpoint should now be set to Custom

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Inference Endpoints (dedicated)