def __init__(
        self,
        metadata: Dict,
        train_set: Union[ItemSet, HeteroItemSet],
        validation_set: Union[ItemSet, HeteroItemSet],
        test_set: Union[ItemSet, HeteroItemSet],
    ):
        """Initialize a task.

        Parameters
        ----------
        metadata : Dict
            Metadata.
        train_set : Union[ItemSet, HeteroItemSet]
            Training set.
        validation_set : Union[ItemSet, HeteroItemSet]
            Validation set.
        test_set : Union[ItemSet, HeteroItemSet]
            Test set.
        """
        self._metadata = metadata
        self._train_set = train_set
        self._validation_set = validation_set
        self._test_set = test_set
Initialize a task.

        Parameters
        ----------
        metadata : Dict
            Metadata.
        train_set : Union[ItemSet, HeteroItemSet]
            Training set.
        validation_set : Union[ItemSet, HeteroItemSet]
            Validation set.
        test_set : Union[ItemSet, HeteroItemSet]
            Test set.
        
python/dgl/graphbolt/impl/ondisk_dataset.py