def build_detection_test_loader(
    dataset: Union[List[Any], torchdata.Dataset],
    *,
    mapper: Callable[[Dict[str, Any]], Any],
    sampler: Optional[torchdata.Sampler] = None,
    batch_size: int = 1,
    num_workers: int = 0,
    collate_fn: Optional[Callable[[List[Any]], Any]] = None,
) -> torchdata.DataLoader:
    """
    Similar to `build_detection_train_loader`, with default batch size = 1,
    and sampler = :class:`InferenceSampler`. This sampler coordinates all workers
    to produce the exact set of all samples.

    Args:
        dataset: a list of dataset dicts,
            or a pytorch dataset (either map-style or iterable). They can be obtained
            by using :func:`DatasetCatalog.get` or :func:`get_detection_dataset_dicts`.
        mapper: a callable which takes a sample (dict) from dataset
           and returns the format to be consumed by the model.
           When using cfg, the default choice is ``DatasetMapper(cfg, is_train=False)``.
        sampler: a sampler that produces
            indices to be applied on ``dataset``. Default to :class:`InferenceSampler`,
            which splits the dataset across all workers. Sampler must be None
            if `dataset` is iterable.
        batch_size: the batch size of the data loader to be created.
            Default to 1 image per worker since this is the standard when reporting
            inference time in papers.
        num_workers: number of parallel data loading workers
        collate_fn: same as the argument of `torch.utils.data.DataLoader`.
            Defaults to do no collation and return a list of data.

    Returns:
        DataLoader: a torch DataLoader, that loads the given detection
        dataset, with test-time transformation and batching.

    Examples:
    ::
        data_loader = build_detection_test_loader(
            DatasetRegistry.get("my_test"),
            mapper=DatasetMapper(...))

        # or, instantiate with a CfgNode:
        data_loader = build_detection_test_loader(cfg, "my_test")
    """
    if isinstance(dataset, list):
        dataset = DatasetFromList(dataset, copy=False)
    if mapper is not None:
        dataset = MapDataset(dataset, mapper)
    if isinstance(dataset, torchdata.IterableDataset):
        assert sampler is None, "sampler must be None if dataset is IterableDataset"
    else:
        if sampler is None:
            sampler = InferenceSampler(len(dataset))
    return torchdata.DataLoader(
        dataset,
        batch_size=batch_size,
        sampler=sampler,
        drop_last=False,
        num_workers=num_workers,
        collate_fn=trivial_batch_collator if collate_fn is None else collate_fn,
    )

    Similar to `build_detection_train_loader`, with default batch size = 1,
    and sampler = :class:`InferenceSampler`. This sampler coordinates all workers
    to produce the exact set of all samples.

    Args:
        dataset: a list of dataset dicts,
            or a pytorch dataset (either map-style or iterable). They can be obtained
            by using :func:`DatasetCatalog.get` or :func:`get_detection_dataset_dicts`.
        mapper: a callable which takes a sample (dict) from dataset
           and returns the format to be consumed by the model.
           When using cfg, the default choice is ``DatasetMapper(cfg, is_train=False)``.
        sampler: a sampler that produces
            indices to be applied on ``dataset``. Default to :class:`InferenceSampler`,
            which splits the dataset across all workers. Sampler must be None
            if `dataset` is iterable.
        batch_size: the batch size of the data loader to be created.
            Default to 1 image per worker since this is the standard when reporting
            inference time in papers.
        num_workers: number of parallel data loading workers
        collate_fn: same as the argument of `torch.utils.data.DataLoader`.
            Defaults to do no collation and return a list of data.

    Returns:
        DataLoader: a torch DataLoader, that loads the given detection
        dataset, with test-time transformation and batching.

    Examples:
    ::
        data_loader = build_detection_test_loader(
            DatasetRegistry.get("my_test"),
            mapper=DatasetMapper(...))

        # or, instantiate with a CfgNode:
        data_loader = build_detection_test_loader(cfg, "my_test")
    
iGPT/models/grit_src/third_party/CenterNet2/detectron2/data/build.py