facebookresearch/detectron2 · error · KeyError

Dataset '{}' is not registered! Available datasets are: {}

Error message

Dataset '{}' is not registered! Available datasets are: {}

What it means

DatasetCatalog.get(name) looks up the registered loader for the dataset name; a KeyError from the lookup is re-raised with a message listing all registered dataset names so you can see what's available.

Source

Thrown at detectron2/data/catalog.py:53

        """
        assert callable(func), "You must register a function with `DatasetCatalog.register`!"
        assert name not in self, "Dataset '{}' is already registered!".format(name)
        self[name] = func

    def get(self, name):
        """
        Call the registered function and return its results.

        Args:
            name (str): the name that identifies a dataset, e.g. "coco_2014_train".

        Returns:
            list[dict]: dataset annotations.
        """
        try:
            f = self[name]
        except KeyError as e:
            raise KeyError(
                "Dataset '{}' is not registered! Available datasets are: {}".format(
                    name, ", ".join(list(self.keys()))
                )
            ) from e
        return f()

    def list(self) -> List[str]:
        """
        List all registered datasets.

        Returns:
            list[str]
        """
        return list(self.keys())

    def remove(self, name):
        """
        Alias of ``pop``.

View on GitHub (pinned to a2f4a8771a)

Solutions

1. Ensure the registering import runs: from my_project import register_datasets before building loaders
2. Fix the dataset name string to exactly match the registration (case-sensitive); the error lists available names
3. If the dataset should be built-in, import detectron2.data.datasets (or the specific builtin module)

Example fix

# before
DatasetCatalog.get("mydata_train")  # not registered
# after
from mydata import register_mydata  # calls DatasetCatalog.register("mydata_train", ...)
register_mydata()
d = DatasetCatalog.get("mydata_train")

from detectron2.data import DatasetCatalog
assert name in DatasetCatalog.list(), f"{name} not registered; have: {DatasetCatalog.list()}"

def dataset_registered(name: str) -> bool:
    return name in DatasetCatalog.list()

try:
    dicts = DatasetCatalog.get(name)
except KeyError as e:
    if "not registered" in str(e):
        import my_datasets  # module that registers
        dicts = DatasetCatalog.get(name)
    else:
        raise

When it happens

Trigger: Calling DatasetCatalog.get('my_train') when only register_instances-style names exist; using cfg.DATASETS.TRAIN=('coco_2017_train_xyz',) with a typo; calling get before your register call ran.

Common situations: Forgetting to import the module that registers the dataset (e.g. custom dataset script); typos in dataset names; expecting built-in registration without importing detectron2.data.datasets.

Related errors

• Attribute '{}' does not exist in the metadata of dataset '{}
• Attribute '{key}' does not exist in the metadata of dataset
• Cannot match one checkpoint key to multiple keys in the mode
• Class with @configurable must have a 'from_config' classmeth
• {name} must take 'cfg' as the first argument!

AI-assisted analysis of facebookresearch/detectron2@a2f4a8771a (2026-08-27). Data as JSON: /api/errors/f992602034e2a7fb. Report an issue: GitHub.