Follow up of #2892 (#3202)

* Follow up of #2892

* typo

* iterabledataset

pytorch_lightning/trainer/data_loading.py

@@ -15,24 +15,18 @@
 import multiprocessing
 import platform
 from abc import ABC, abstractmethod
-from distutils.version import LooseVersion
 from typing import Union, List, Tuple, Callable, Optional
 
-import torch
 import torch.distributed as torch_distrib
 from torch.utils.data import DataLoader, RandomSampler, SequentialSampler
 from torch.utils.data.distributed import DistributedSampler
 
 from pytorch_lightning.core import LightningModule
 from pytorch_lightning.utilities import rank_zero_warn
+from pytorch_lightning.utilities.data import has_iterable_dataset, has_len
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.debugging import InternalDebugger
 
-try:
-    from torch.utils.data import IterableDataset
-    ITERABLE_DATASET_EXISTS = True
-except ImportError:
-    ITERABLE_DATASET_EXISTS = False
 
 try:
     from apex import amp
@@ -56,35 +50,6 @@
     HOROVOD_AVAILABLE = True
 
 
-def _has_iterable_dataset(dataloader: DataLoader):
-    return ITERABLE_DATASET_EXISTS and hasattr(dataloader, 'dataset') \
-        and isinstance(dataloader.dataset, IterableDataset)
-
-
-def _has_len(dataloader: DataLoader) -> bool:
-    """ Checks if a given Dataloader has __len__ method implemented i.e. if
-    it is a finite dataloader or infinite dataloader. """
-
-    try:
-        # try getting the length
-        if len(dataloader) == 0:
-            raise ValueError('`Dataloader` returned 0 length.'
-                             ' Please make sure that your Dataloader at least returns 1 batch')
-        has_len = True
-    except TypeError:
-        has_len = False
-    except NotImplementedError:  # e.g. raised by torchtext if a batch_size_fn is used
-        has_len = False
-
-    if has_len and _has_iterable_dataset(dataloader) and LooseVersion(torch.__version__) >= LooseVersion("1.4.0"):
-        rank_zero_warn(
-            'Your `IterableDataset` has `__len__` defined.'
-            ' In combination with multi-processing data loading (e.g. batch size > 1),'
-            ' this can lead to unintended side effects since the samples will be duplicated.'
-        )
-    return has_len
-
-
 class TrainerDataLoadingMixin(ABC):
 
     # this is just a summary on variables used in this abstract class,
@@ -147,7 +112,7 @@ def auto_add_sampler(self, dataloader: DataLoader, train: bool) -> DataLoader:
         # don't do anything if it's not a dataloader
         is_dataloader = isinstance(dataloader, DataLoader)
         # don't manipulate iterable datasets
-        is_iterable_ds = _has_iterable_dataset(dataloader)
+        is_iterable_ds = has_iterable_dataset(dataloader)
 
         if not is_dataloader or is_iterable_ds:
             return dataloader
@@ -214,7 +179,7 @@ def reset_train_dataloader(self, model: LightningModule) -> None:
         # automatically add samplers
         self.train_dataloader = self.auto_add_sampler(self.train_dataloader, train=True)
 
-        self.num_training_batches = len(self.train_dataloader) if _has_len(self.train_dataloader) else float('inf')
+        self.num_training_batches = len(self.train_dataloader) if has_len(self.train_dataloader) else float('inf')
         self._worker_check(self.train_dataloader, 'train dataloader')
 
         if isinstance(self.limit_train_batches, int) or self.limit_train_batches == 0.0:
@@ -238,7 +203,7 @@ def reset_train_dataloader(self, model: LightningModule) -> None:
                     f'to the number of the training batches ({self.num_training_batches}). '
                     'If you want to disable validation set `limit_val_batches` to 0.0 instead.')
         else:
-            if not _has_len(self.train_dataloader):
+            if not has_len(self.train_dataloader):
                 if self.val_check_interval == 1.0:
                     self.val_check_batch = float('inf')
                 else:
@@ -305,7 +270,7 @@ def _reset_eval_dataloader(
         # datasets could be none, 1 or 2+
         if len(dataloaders) != 0:
             for i, dataloader in enumerate(dataloaders):
-                num_batches = len(dataloader) if _has_len(dataloader) else float('inf')
+                num_batches = len(dataloader) if has_len(dataloader) else float('inf')
                 self._worker_check(dataloader, f'{mode} dataloader {i}')
 
                 # percent or num_steps

pytorch_lightning/utilities/data.py

@@ -0,0 +1,47 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from distutils.version import LooseVersion
+import torch
+from torch.utils.data import DataLoader, IterableDataset
+
+from pytorch_lightning.utilities import rank_zero_warn
+
+
+def has_iterable_dataset(dataloader: DataLoader):
+    return hasattr(dataloader, 'dataset') and isinstance(dataloader.dataset, IterableDataset)
+
+
+def has_len(dataloader: DataLoader) -> bool:
+    """ Checks if a given Dataloader has __len__ method implemented i.e. if
+    it is a finite dataloader or infinite dataloader. """
+
+    try:
+        # try getting the length
+        if len(dataloader) == 0:
+            raise ValueError('`Dataloader` returned 0 length.'
+                             ' Please make sure that your Dataloader at least returns 1 batch')
+        has_len = True
+    except TypeError:
+        has_len = False
+    except NotImplementedError:  # e.g. raised by torchtext if a batch_size_fn is used
+        has_len = False
+
+    if has_len and has_iterable_dataset(dataloader) and LooseVersion(torch.__version__) >= LooseVersion("1.4.0"):
+        rank_zero_warn(
+            'Your `IterableDataset` has `__len__` defined.'
+            ' In combination with multi-processing data loading (e.g. batch size > 1),'
+            ' this can lead to unintended side effects since the samples will be duplicated.'
+        )
+    return has_len

tests/trainer/test_dataloaders.py

@@ -11,7 +11,7 @@
 
 import tests.base.develop_pipelines as tpipes
 from pytorch_lightning import Trainer, Callback
-from pytorch_lightning.trainer.data_loading import _has_iterable_dataset, _has_len
+from pytorch_lightning.utilities.data import has_iterable_dataset, has_len
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from tests.base import EvalModelTemplate
 
@@ -624,7 +624,7 @@ def test_warning_with_few_workers(mock, tmpdir, ckpt_path):
     reason="IterableDataset with __len__ before 1.4 raises",
 )
 def test_warning_with_iterable_dataset_and_len(tmpdir):
-    """ Tests that a warning messages is shown when an IterableDataset defines `__len__`. """
+    """ Tests that a warning message is shown when an IterableDataset defines `__len__`. """
     model = EvalModelTemplate()
     original_dataset = model.train_dataloader().dataset
 
@@ -637,8 +637,8 @@ def __len__(self):
             return len(original_dataset)
 
     dataloader = DataLoader(IterableWithLen(), batch_size=16)
-    assert _has_len(dataloader)
-    assert _has_iterable_dataset(dataloader)
+    assert has_len(dataloader)
+    assert has_iterable_dataset(dataloader)
     trainer = Trainer(
         default_root_dir=tmpdir,
         max_steps=3,