#
How to contribute a community pipeline

💡 Take a look at GitHub Issue #841 for more context about why we’re adding community pipelines to help everyone easily share their work without being slowed down.

Community pipelines allow you to add any additional features you’d like on top of the DiffusionPipeline. The main benefit of building on top of the `DiffusionPipeline` is anyone can load and use your pipeline by only adding one more argument, making it super easy for the community to access.

This guide will show you how to create a community pipeline and explain how they work. To keep things simple, you’ll create a “one-step” pipeline where the `UNet` does a single forward pass and calls the scheduler once.

##
Initialize the pipeline

You should start by creating a `one_step_unet.py` file for your community pipeline. In this file, create a pipeline class that inherits from the DiffusionPipeline to be able to load model weights and the scheduler configuration from the Hub. The one-step pipeline needs a `UNet` and a scheduler, so you’ll need to add these as arguments to the `__init__` function:

    from diffusers import DiffusionPipeline
    import torch

    class UnetSchedulerOneForwardPipeline(DiffusionPipeline):
        def __init__(self, unet, scheduler):
            super().__init__()

To ensure your pipeline and its components (`unet` and `scheduler`) can be saved with save_pretrained(), add them to the `register_modules` function:

      from diffusers import DiffusionPipeline
      import torch

      class UnetSchedulerOneForwardPipeline(DiffusionPipeline):
          def __init__(self, unet, scheduler):
              super().__init__()

    +         self.register_modules(unet=unet, scheduler=scheduler)

Cool, the `__init__` step is done and you can move to the forward pass now! 🔥

##
Define the forward pass

In the forward pass, which we recommend defining as `__call__`, you have complete creative freedom to add whatever feature you’d like. For our amazing one-step pipeline, create a random image and only call the `unet` and `scheduler` once by setting `timestep=1`:

      from diffusers import DiffusionPipeline
      import torch

      class UnetSchedulerOneForwardPipeline(DiffusionPipeline):
          def __init__(self, unet, scheduler):
              super().__init__()

              self.register_modules(unet=unet, scheduler=scheduler)

    +     def __call__(self):
    +         image = torch.randn(
    +             (1, self.unet.config.in_channels, self.unet.config.sample_size, self.unet.config.sample_size),
    +         )
    +         timestep = 1

    +         model_output = self.unet(image, timestep).sample
    +         scheduler_output = self.scheduler.step(model_output, timestep, image).prev_sample

    +         return scheduler_output

That’s it! 🚀 You can now run this pipeline by passing a `unet` and `scheduler` to it:

    from diffusers import DDPMScheduler, UNet2DModel

    scheduler = DDPMScheduler()
    unet = UNet2DModel()

    pipeline = UnetSchedulerOneForwardPipeline(unet=unet, scheduler=scheduler)

    output = pipeline()

But what’s even better is you can load pre-existing weights into the pipeline if the pipeline structure is identical. For example, you can load the `google/ddpm-cifar10-32` weights into the one-step pipeline:

    pipeline = UnetSchedulerOneForwardPipeline.from_pretrained("google/ddpm-cifar10-32", use_safetensors=True)

    output = pipeline()

##
Share your pipeline

Open a Pull Request on the 🧨 Diffusers repository to add your awesome pipeline in `one_step_unet.py` to the examples/community subfolder.

Once it is merged, anyone with `diffusers >= 0.4.0` installed can use this pipeline magically 🪄 by specifying it in the `custom_pipeline` argument:

    from diffusers import DiffusionPipeline

    pipe = DiffusionPipeline.from_pretrained(
        "google/ddpm-cifar10-32", custom_pipeline="one_step_unet", use_safetensors=True
    )
    pipe()

Another way to share your community pipeline is to upload the `one_step_unet.py` file directly to your preferred model repository on the Hub. Instead of specifying the `one_step_unet.py` file, pass the model repository id to the `custom_pipeline` argument:

    from diffusers import DiffusionPipeline

    pipeline = DiffusionPipeline.from_pretrained(
        "google/ddpm-cifar10-32", custom_pipeline="stevhliu/one_step_unet", use_safetensors=True
    )

Take a look at the following table to compare the two sharing workflows to help you decide the best option for you:

| GitHub community pipeline | HF Hub community pipeline
--- | --- | ---
usage | same | same
review process | open a Pull Request on GitHub and undergo a review process from the Diffusers team before merging; may be slower | upload directly to a Hub repository without any review; this is the fastest workflow
visibility | included in the official Diffusers repository and documentation | included on your HF Hub profile and relies on your own usage/promotion to gain visibility

💡 You can use whatever package you want in your community pipeline file - as long as the user has it installed, everything will work fine. Make sure you have one and only one pipeline class that inherits from `DiffusionPipeline` because this is automatically detected.

##
How do community pipelines work?

A community pipeline is a class that inherits from DiffusionPipeline which means:

- It can be loaded with the `custom_pipeline` argument.
- The model weights and scheduler configuration are loaded from `pretrained_model_name_or_path`.
- The code that implements a feature in the community pipeline is defined in a `pipeline.py` file.

Sometimes you can’t load all the pipeline components weights from an official repository. In this case, the other components should be passed directly to the pipeline:

    from diffusers import DiffusionPipeline
    from transformers import CLIPFeatureExtractor, CLIPModel

    model_id = "CompVis/stable-diffusion-v1-4"
    clip_model_id = "laion/CLIP-ViT-B-32-laion2B-s34B-b79K"

    feature_extractor = CLIPFeatureExtractor.from_pretrained(clip_model_id)
    clip_model = CLIPModel.from_pretrained(clip_model_id, torch_dtype=torch.float16)

    pipeline = DiffusionPipeline.from_pretrained(
        model_id,
        custom_pipeline="clip_guided_stable_diffusion",
        clip_model=clip_model,
        feature_extractor=feature_extractor,
        scheduler=scheduler,
        torch_dtype=torch.float16,
        use_safetensors=True,
    )

The magic behind community pipelines is contained in the following code. It allows the community pipeline to be loaded from GitHub or the Hub, and it’ll be available to all 🧨 Diffusers packages.

    # 2. Load the pipeline class, if using custom module then load it from the hub
    # if we load from explicit class, let's use it
    if custom_pipeline is not None:
        pipeline_class = get_class_from_dynamic_module(
            custom_pipeline, module_file=CUSTOM_PIPELINE_FILE_NAME, cache_dir=custom_pipeline
        )
    elif cls != DiffusionPipeline:
        pipeline_class = cls
    else:
        diffusers_module = importlib.import_module(cls.__module__.split(".")[0])
        pipeline_class = getattr(diffusers_module, config_dict["_class_name"])