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, :attr:`shuffle` must not be specified. batch_sampler (Sampler or Iterable, optional): like :attr:`sampler`, but returns a batch of indices at a time. Mutually exclusive with :attr:`batch_size`, :attr:`shuffle`, :attr:`sampler`, and :attr:`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 :attr:`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`_ 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): the device to :attr:`pin_memory` to if ``pin_memory`` is ``True``. .. warning:: If the ``spawn`` start method is used, :attr:`worker_init_fn` cannot be an unpicklable object, e.g., a lambda function. See :ref:`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 :attr:`dataset` is an :class:`~torch.utils.data.IterableDataset`, it instead returns an estimate based on ``len(dataset) / batch_size``, with proper rounding depending on :attr:`drop_last`, regardless of multi-process loading configurations. This represents the best guess PyTorch can make because PyTorch trusts user :attr:`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 :attr:`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 :class:`~torch.utils.data.IterableDataset` interacts with `Multi-process data loading`_. .. warning:: See :ref:`reproducibility`, and :ref:`dataloader-workers-random-seed`, and :ref:`data-loading-randomness` notes for random seed related questions. .. _multiprocessing context: https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods r#