pytorch_pfn_extras.dataloaders.dataloader.DataLoader#

class pytorch_pfn_extras.dataloaders.dataloader.DataLoader(dataset, batch_size=1, shuffle=None, sampler=None, batch_sampler=None, num_workers=0, collate_fn=None, pin_memory=False, drop_last=False, timeout=0, worker_init_fn=None, multiprocessing_context=None, generator=None, *, prefetch_factor=None, persistent_workers=False, pin_memory_device='', in_order=True)#

Bases: Generic[_T_co]

Data loader combines a dataset and a sampler, and provides an iterable over the given dataset.

The DataLoader supports both map-style and iterable-style datasets with single- or multi-process loading, customizing loading order and optional automatic batching (collation) and memory pinning.

See torch.utils.data documentation page for more details.

Parameters:

  • dataset (Dataset) – dataset from which to load the data.

  • batch_size (int, optional) – how many samples per batch to load (default: 1).

  • shuffle (bool, optional) – set to True to have the data reshuffled at every epoch (default: False).

  • sampler (Sampler or Iterable, optional) – defines the strategy to draw samples from the dataset. Can be any Iterable with __len__ implemented. If specified, shuffle must not be specified.

  • batch_sampler (Sampler or Iterable, optional) – like sampler, but returns a batch of indices at a time. Mutually exclusive with batch_size, shuffle, sampler, and drop_last.

  • num_workers (int, optional) – how many subprocesses to use for data loading. 0 means that the data will be loaded in the main process. (default: 0)

  • collate_fn (Callable, optional) – merges a list of samples to form a mini-batch of Tensor(s). Used when using batched loading from a map-style dataset.

  • pin_memory (bool, optional) – If True, the data loader will copy Tensors into device/CUDA pinned memory before returning them. If your data elements are a custom type, or your collate_fn returns a batch that is a custom type, see the example below.

  • drop_last (bool, optional) – set to True to drop the last incomplete batch, if the dataset size is not divisible by the batch size. If False and the size of dataset is not divisible by the batch size, then the last batch will be smaller. (default: False)

  • timeout (numeric, optional) – if positive, the timeout value for collecting a batch from workers. Should always be non-negative. (default: 0)

  • worker_init_fn (Callable, optional) – If not None, this will be called on each worker subprocess with the worker id (an int in [0, num_workers - 1]) as input, after seeding and before data loading. (default: None)

  • multiprocessing_context (str or multiprocessing.context.BaseContext, optional) – If None, the default multiprocessing context # noqa: D401 of your operating system will be used. (default: None)

  • generator (torch.Generator, optional) – If not None, this RNG will be used by RandomSampler to generate random indexes and multiprocessing to generate base_seed for workers. (default: None)

  • prefetch_factor (int, optional, keyword-only arg) – Number of batches loaded in advance by each worker. 2 means there will be a total of 2 * num_workers batches prefetched across all workers. (default value depends on the set value for num_workers. If value of num_workers=0 default is None. Otherwise, if value of num_workers > 0 default is 2).

  • persistent_workers (bool, optional) – If True, the data loader will not shut down the worker processes after a dataset has been consumed once. This allows to maintain the workers Dataset instances alive. (default: False)

  • pin_memory_device (str, optional) – Deprecated, the current accelerator will be used as the device if pin_memory=True.

  • in_order (bool, optional) – If False, the data loader will not enforce that batches are returned in a first-in, first-out order. Only applies when num_workers > 0. (default: True)

Warning

If the spawn start method is used, worker_init_fn cannot be an unpicklable object, e.g., a lambda function. See multiprocessing-best-practices on more details related to multiprocessing in PyTorch.

Warning

len(dataloader) heuristic is based on the length of the sampler used. When dataset is an IterableDataset, it instead returns an estimate based on len(dataset) / batch_size, with proper rounding depending on drop_last, regardless of multi-process loading configurations. This represents the best guess PyTorch can make because PyTorch trusts user dataset code in correctly handling multi-process loading to avoid duplicate data.

However, if sharding results in multiple workers having incomplete last batches, this estimate can still be inaccurate, because (1) an otherwise complete batch can be broken into multiple ones and (2) more than one batch worth of samples can be dropped when drop_last is set. Unfortunately, PyTorch can not detect such cases in general.

See `Dataset Types`_ for more details on these two types of datasets and how IterableDataset interacts with `Multi-process data loading`_.

Warning

See reproducibility, and dataloader-workers-random-seed, and data-loading-randomness notes for random seed related questions.

Warning

Setting in_order to False can harm reproducibility and may lead to a skewed data distribution being fed to the trainer in cases with imbalanced data.

Methods

__init__(dataset[, batch_size, shuffle, ...])

check_worker_number_rationality()

Attributes

multiprocessing_context

dataset

batch_size

num_workers

pin_memory

drop_last

timeout

sampler

pin_memory_device

prefetch_factor

__init__(dataset, batch_size=1, shuffle=None, sampler=None, batch_sampler=None, num_workers=0, collate_fn=None, pin_memory=False, drop_last=False, timeout=0, worker_init_fn=None, multiprocessing_context=None, generator=None, *, prefetch_factor=None, persistent_workers=False, pin_memory_device='', in_order=True)#
Parameters:

  • dataset (Dataset[_T_co]) –

  • batch_size (int | None) –

  • shuffle (bool | None) –

  • sampler (Sampler | Iterable | None) –

  • batch_sampler (Sampler[list] | Iterable[list] | None) –

  • num_workers (int) –

  • collate_fn (_collate_fn_t | None) –

  • pin_memory (bool) –

  • drop_last (bool) –

  • timeout (float) –

  • worker_init_fn (_worker_init_fn_t | None) –

  • prefetch_factor (int | None) –

  • persistent_workers (bool) –

  • pin_memory_device (str) –

  • in_order (bool) –

Return type:

None

batch_size: int | None#
check_worker_number_rationality()#
Return type:

None

dataset: Dataset[_T_co]#
drop_last: bool#
property multiprocessing_context#
num_workers: int#
pin_memory: bool#
pin_memory_device: str#
prefetch_factor: int | None#
sampler: Sampler | Iterable#
timeout: float#