Ref: Pull duplicate data interface definition up into DataHooks class (…

…#3344)

* pull data hooks up into a common interface

* fix multiple inheritance ordering

* docs reference datahooks

docs/source/lightning-module.rst

@@ -1239,5 +1239,5 @@ teardown
 transfer_batch_to_device
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-.. autofunction:: pytorch_lightning.core.hooks.ModelHooks.transfer_batch_to_device
+.. autofunction:: pytorch_lightning.core.hooks.DataHooks.transfer_batch_to_device
     :noindex:

pytorch_lightning/core/datamodule.py

@@ -21,7 +21,8 @@
 import torch
 from torch.utils.data import DataLoader
 
-from pytorch_lightning.utilities import parsing, rank_zero_only, rank_zero_warn
+from pytorch_lightning.core.hooks import DataHooks
+from pytorch_lightning.utilities import parsing, rank_zero_only
 
 
 class _DataModuleWrapper(type):
@@ -87,7 +88,7 @@ def wrapped_fn(*args, **kwargs):
     return wrapped_fn
 
 
-class LightningDataModule(object, metaclass=_DataModuleWrapper):  # pragma: no cover
+class LightningDataModule(DataHooks, metaclass=_DataModuleWrapper):
     """
     A DataModule standardizes the training, val, test splits, data preparation and transforms.
     The main advantage is consistent data splits, data preparation and transforms across models.
@@ -215,147 +216,27 @@ def has_setup_test(self):
 
     @abstractmethod
     def prepare_data(self, *args, **kwargs):
-        """
-        Use this to download and prepare data.
-        In distributed (GPU, TPU), this will only be called once.
-
-        .. warning:: Do not assign anything to the datamodule in this step since this will only be called on 1 GPU.
-
-        Pseudocode::
-
-            dm.prepare_data()
-            dm.setup()
-
-        Example::
-
-            def prepare_data(self):
-                download_imagenet()
-                clean_imagenet()
-                cache_imagenet()
-        """
+        pass
 
     @abstractmethod
     def setup(self, stage: Optional[str] = None):
-        """
-        Use this to load your data from file, split it, etc. You are safe to make state assignments here.
-        This hook is called on every process when using DDP.
-
-        Example::
-
-            def setup(self, stage):
-                data = load_data(...)
-                self.train_ds, self.val_ds, self.test_ds = split_data(data)
-        """
+        pass
 
     @abstractmethod
     def train_dataloader(self, *args, **kwargs) -> DataLoader:
-        """
-        Implement a PyTorch DataLoader for training.
-        Return:
-            Single PyTorch :class:`~torch.utils.data.DataLoader`.
-        Note:
-            Lightning adds the correct sampler for distributed and arbitrary hardware.
-            There is no need to set it yourself.
-
-        Example::
-
-            def train_dataloader(self):
-                dataset = MNIST(root=PATH, train=True, transform=transforms.ToTensor(), download=False)
-                loader = torch.utils.data.DataLoader(dataset=dataset)
-                return loader
-
-        """
-        rank_zero_warn('`train_dataloader` must be implemented to be used with the Lightning Trainer')
+        pass
 
     @abstractmethod
     def val_dataloader(self, *args, **kwargs) -> Union[DataLoader, List[DataLoader]]:
-        r"""
-        Implement a PyTorch DataLoader for training.
-        Return:
-            Single PyTorch :class:`~torch.utils.data.DataLoader`.
-        Note:
-            Lightning adds the correct sampler for distributed and arbitrary hardware.
-            There is no need to set it yourself.
-        Note:
-            You can also return a list of DataLoaders
-
-        Example::
-
-            def val_dataloader(self):
-                dataset = MNIST(root=PATH, train=False, transform=transforms.ToTensor(), download=False)
-                loader = torch.utils.data.DataLoader(dataset=dataset, shuffle=False)
-                return loader
-        """
+        pass
 
     @abstractmethod
     def test_dataloader(self, *args, **kwargs) -> Union[DataLoader, List[DataLoader]]:
-        r"""
-        Implement a PyTorch DataLoader for training.
-        Return:
-            Single PyTorch :class:`~torch.utils.data.DataLoader`.
-        Note:
-            Lightning adds the correct sampler for distributed and arbitrary hardware.
-            There is no need to set it yourself.
-        Note:
-            You can also return a list of DataLoaders
-
-        Example::
-
-            def test_dataloader(self):
-                dataset = MNIST(root=PATH, train=False, transform=transforms.ToTensor(), download=False)
-                loader = torch.utils.data.DataLoader(dataset=dataset, shuffle=False)
-                return loader
-        """
+        pass
 
     @abstractmethod
     def transfer_batch_to_device(self, batch: Any, device: torch.device) -> Any:
-        """
-        Override this hook if your :class:`~torch.utils.data.DataLoader` returns tensors
-        wrapped in a custom data structure.
-
-        The data types listed below (and any arbitrary nesting of them) are supported out of the box:
-
-        - :class:`torch.Tensor` or anything that implements `.to(...)`
-        - :class:`list`
-        - :class:`dict`
-        - :class:`tuple`
-        - :class:`torchtext.data.batch.Batch`
-
-        For anything else, you need to define how the data is moved to the target device (CPU, GPU, TPU, ...).
-
-        Example::
-
-            def transfer_batch_to_device(self, batch, device)
-                if isinstance(batch, CustomBatch):
-                    # move all tensors in your custom data structure to the device
-                    batch.samples = batch.samples.to(device)
-                    batch.targets = batch.targets.to(device)
-                else:
-                    batch = super().transfer_batch_to_device(data, device)
-                return batch
-
-        Args:
-            batch: A batch of data that needs to be transferred to a new device.
-            device: The target device as defined in PyTorch.
-
-        Returns:
-            A reference to the data on the new device.
-
-        Note:
-            This hook should only transfer the data and not modify it, nor should it move the data to
-            any other device than the one passed in as argument (unless you know what you are doing).
-
-        Note:
-            This hook only runs on single GPU training (no data-parallel). If you need multi-GPU support
-            for your custom batch objects, you need to define your custom
-            :class:`~torch.nn.parallel.DistributedDataParallel` or
-            :class:`~pytorch_lightning.overrides.data_parallel.LightningDistributedDataParallel` and
-            override :meth:`~pytorch_lightning.core.lightning.LightningModule.configure_ddp`.
-
-        See Also:
-            - :func:`~pytorch_lightning.utilities.apply_func.move_data_to_device`
-            - :func:`~pytorch_lightning.utilities.apply_func.apply_to_collection`
-        """
+        pass
 
     @classmethod
     def add_argparse_args(cls, parent_parser: ArgumentParser) -> ArgumentParser: