diffusers/docs/source/en/modular_diffusers/auto_docstring.md

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# Auto docstring and parameter templates

Every [`~modular_pipelines.ModularPipelineBlocks`] has a `doc` property that is automatically generated from its `description`, `inputs`, `intermediate_outputs`, `expected_components`, and `expected_configs`. The auto docstring system keeps docstrings in sync with the block's actual interface. Parameter templates provide standardized descriptions for parameters that appear across many pipelines.

## Auto docstring

Modular pipeline blocks are composable — you can nest them, chain them in sequences, and rearrange them freely. Their docstrings follow the same pattern. When a [`~modular_pipelines.SequentialPipelineBlocks`] aggregates inputs and outputs from its sub-blocks, the documentation should update automatically without manual rewrites.

The `# auto_docstring` marker generates docstrings from the block's properties. Add it above a class definition to mark the class for automatic docstring generation.

```py
# auto_docstring
class FluxTextEncoderStep(SequentialPipelineBlocks):
    ...
```

Run the following command to generate and insert the docstrings.

```bash
python utils/modular_auto_docstring.py --fix_and_overwrite
```

The utility reads the block's `doc` property and inserts it as the class docstring.

```py
# auto_docstring
class FluxTextEncoderStep(SequentialPipelineBlocks):
    """
    Text input processing step that standardizes text embeddings for the pipeline.

    Inputs:
        prompt_embeds (`torch.Tensor`) *required*:
            text embeddings used to guide the image generation.
        ...

    Outputs:
        prompt_embeds (`torch.Tensor`):
            text embeddings used to guide the image generation.
        ...
    """
```

You can also check without overwriting, or target a specific file or directory.

```bash
# Check that all marked classes have up-to-date docstrings
python utils/modular_auto_docstring.py

# Check a specific file or directory
python utils/modular_auto_docstring.py src/diffusers/modular_pipelines/flux/
```

If any marked class is missing a docstring, the check fails and lists the classes that need updating.

```
Found the following # auto_docstring markers that need docstrings:
- src/diffusers/modular_pipelines/flux/encoders.py: FluxTextEncoderStep at line 42

Run `python utils/modular_auto_docstring.py --fix_and_overwrite` to fix them.
```

## Parameter templates

`InputParam` and `OutputParam` define a block's inputs and outputs. Create them directly or use `.template()` for standardized definitions of common parameters like `prompt`, `num_inference_steps`, or `latents`.

### InputParam

[`~modular_pipelines.InputParam`] describes a single input to a block.

| Field | Type | Description |
|---|---|---|
| `name` | `str` | Name of the parameter |
| `type_hint` | `Any` | Type annotation (e.g., `str`, `torch.Tensor`) |
| `default` | `Any` | Default value (if not set, parameter has no default) |
| `required` | `bool` | Whether the parameter is required |
| `description` | `str` | Human-readable description |
| `kwargs_type` | `str` | Group name for related parameters (e.g., `"denoiser_input_fields"`) |
| `metadata` | `dict` | Arbitrary additional information |

#### Creating InputParam directly

```py
from diffusers.modular_pipelines import InputParam

InputParam(
    name="guidance_scale",
    type_hint=float,
    default=7.5,
    description="Scale for classifier-free guidance.",
)
```

#### Using a template

```py
InputParam.template("prompt")
# Equivalent to:
# InputParam(name="prompt", type_hint=str, required=True,
#            description="The prompt or prompts to guide image generation.")
```

Templates set `name`, `type_hint`, `default`, `required`, and `description` automatically. Override any field or add context with the `note` parameter.

```py
# Override the default value
InputParam.template("num_inference_steps", default=28)

# Add a note to the description
InputParam.template("prompt_embeds", note="batch-expanded")
# description becomes: "text embeddings used to guide the image generation. ... (batch-expanded)"
```

### OutputParam

[`~modular_pipelines.OutputParam`] describes a single output from a block.

| Field | Type | Description |
|---|---|---|
| `name` | `str` | Name of the parameter |
| `type_hint` | `Any` | Type annotation |
| `description` | `str` | Human-readable description |
| `kwargs_type` | `str` | Group name for related parameters |
| `metadata` | `dict` | Arbitrary additional information |

#### Creating OutputParam directly

```py
from diffusers.modular_pipelines import OutputParam

OutputParam(name="image_latents", type_hint=torch.Tensor, description="Encoded image latents.")
```

#### Using a template

```py
OutputParam.template("latents")

# Add a note to the description
OutputParam.template("prompt_embeds", note="batch-expanded")
```

## Available templates

`INPUT_PARAM_TEMPLATES` and `OUTPUT_PARAM_TEMPLATES` are defined in [modular_pipeline_utils.py](https://github.com/huggingface/diffusers/blob/main/src/diffusers/modular_pipelines/modular_pipeline_utils.py). They include common parameters like `prompt`, `image`, `num_inference_steps`, `latents`, `prompt_embeds`, and more. Refer to the source for the full list of available template names.