huggingface/transformers · error · ValueError

{auto_class} is not a valid auto class.

Error message

{auto_class} is not a valid auto class.

What it means

Error "{auto_class} is not a valid auto class." thrown in huggingface/transformers.

Source

Thrown at src/transformers/image_processing_base.py:469

    @classmethod
    def register_for_auto_class(cls, auto_class="AutoImageProcessor"):
        """
        Register this class with a given auto class. This should only be used for custom image processors as the ones
        in the library are already mapped with `AutoImageProcessor `.



        Args:
            auto_class (`str` or `type`, *optional*, defaults to `"AutoImageProcessor "`):
                The auto class to register this new image processor with.
        """
        if not isinstance(auto_class, str):
            auto_class = auto_class.__name__

        import transformers.models.auto as auto_module

        if not hasattr(auto_module, auto_class):
            raise ValueError(f"{auto_class} is not a valid auto class.")

        cls._auto_class = auto_class

    def fetch_images(self, image_url_or_urls: str | list[str] | list[list[str]]):
        """
        Convert a single or a list of urls into the corresponding `PIL.Image` objects.

        If a single url is passed, the return value will be a single object. If a list is passed a list of objects is
        returned.
        """
        if isinstance(image_url_or_urls, (list, tuple)):
            return [self.fetch_images(x) for x in image_url_or_urls]
        elif isinstance(image_url_or_urls, str):
            return load_image(image_url_or_urls)
        elif is_valid_image(image_url_or_urls):
            return image_url_or_urls
        else:
            raise TypeError(f"only a single or a list of entries is supported but got type={type(image_url_or_urls)}")

View on GitHub (pinned to a597f97485)

Solutions

1. Use a valid auto class name such as 'AutoImageProcessor'.
2. Check the registered auto class names in the mapping.

When it happens

Trigger: Raised in ImageProcessingMixin.from_dict/from_json auto-class resolution when auto_class is not a registered auto class name.

Common situations: Typo or unsupported value in the auto_class argument when loading an image processor generically.

AI-assisted analysis of huggingface/transformers@a597f97485 (2026-08-14). Data as JSON: /api/errors/65b8cb91b60007ce. Report an issue: GitHub.