Revert "Add support for `len(datamodule)` (#9895)" (#10072)

This reverts commit 6429de8944.

CHANGELOG.md

@@ -187,9 +187,6 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added support for `torch.autograd.set_detect_anomaly` through `Trainer` constructor argument `detect_anomaly` ([#9848](https://github.com/PyTorchLightning/pytorch-lightning/pull/9848))
 
 
-- Added a `len` method to `LightningDataModule` ([#9895](https://github.com/PyTorchLightning/pytorch-lightning/pull/9895))
-
-
 - Added `enable_model_summary` flag to Trainer ([#9699](https://github.com/PyTorchLightning/pytorch-lightning/pull/9699))
 
 

pytorch_lightning/core/datamodule.py

@@ -22,10 +22,7 @@ from torch.utils.data import DataLoader, Dataset, IterableDataset
 from pytorch_lightning.core.hooks import CheckpointHooks, DataHooks
 from pytorch_lightning.core.mixins import HyperparametersMixin
 from pytorch_lightning.utilities import rank_zero_deprecation
-from pytorch_lightning.utilities.apply_func import apply_to_collection
 from pytorch_lightning.utilities.argparse import add_argparse_args, from_argparse_args, get_init_arguments_and_types
-from pytorch_lightning.utilities.data import has_len
-from pytorch_lightning.utilities.warnings import rank_zero_warn
 
 
 class LightningDataModule(CheckpointHooks, DataHooks, HyperparametersMixin):
@@ -484,40 +481,3 @@ class LightningDataModule(CheckpointHooks, DataHooks, HyperparametersMixin):
         for fn in ("prepare_data", "setup", "teardown"):
             del d[fn]
         return d
-
-    def __len__(self) -> int:
-        """Returns the total number of batches in all dataloaders defined in the datamodule."""
-
-        from pytorch_lightning.trainer.supporters import CombinedLoader
-
-        num_batches = 0
-        not_implemented_count = 0
-
-        def get_num_batches(dataloader: DataLoader, name: str) -> None:
-            nonlocal num_batches
-            if not has_len(dataloader):
-                rank_zero_warn(
-                    f"The number of batches for a dataloader in `{name}` is counted as 0 "
-                    "because it does not have `__len__` defined."
-                )
-            else:
-                num_batches += len(dataloader)
-
-        for method_name in ("train_dataloader", "val_dataloader", "test_dataloader", "predict_dataloader"):
-            dataloader_method = getattr(self, method_name)
-            if not callable(dataloader_method):
-                not_implemented_count += 1
-                continue
-            try:
-                dataloader = dataloader_method()
-            except NotImplementedError:
-                not_implemented_count += 1
-                continue
-            if isinstance(dataloader, CombinedLoader):
-                dataloader = dataloader.loaders
-            apply_to_collection(dataloader, DataLoader, get_num_batches, method_name)
-
-        if not_implemented_count == 4:
-            rank_zero_warn("You datamodule does not have any valid dataloader so `__len__` will be returned as 0.")
-
-        return num_batches

tests/core/test_datamodules.py

@@ -21,15 +21,13 @@ from unittest.mock import call, PropertyMock
 import pytest
 import torch
 from omegaconf import OmegaConf
-from torch.utils.data import DataLoader
 
 from pytorch_lightning import LightningDataModule, Trainer
 from pytorch_lightning.callbacks import ModelCheckpoint
-from pytorch_lightning.trainer.supporters import CombinedLoader
 from pytorch_lightning.utilities import AttributeDict
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.model_helpers import is_overridden
-from tests.helpers import BoringDataModule, BoringModel, RandomDataset
+from tests.helpers import BoringDataModule, BoringModel
 from tests.helpers.datamodules import ClassifDataModule
 from tests.helpers.runif import RunIf
 from tests.helpers.simple_models import ClassificationModel
@@ -566,14 +564,13 @@ def test_define_as_dataclass():
         batch_size: int
         dims: int = 2
 
-        def train_dataloader(self):
+        def __post_init__(self):
-            return DataLoader(torch.randn(self.batch_size * 2, 10), batch_size=self.batch_size)
+            super().__init__(dims=self.dims)
 
     # asserts for the different dunder methods added by dataclass, when __init__ is implemented, i.e.
     # __repr__, __eq__, __lt__, __le__, etc.
     assert BoringDataModule1(batch_size=64).dims == 2
     assert BoringDataModule1(batch_size=32)
-    assert len(BoringDataModule1(batch_size=32)) == 2
     assert hasattr(BoringDataModule1, "__repr__")
     assert BoringDataModule1(batch_size=32) == BoringDataModule1(batch_size=32)
 
@@ -584,9 +581,7 @@ def test_define_as_dataclass():
 
     # asserts for the different dunder methods added by dataclass, when super class is inherently initialized, i.e.
     # __init__, __repr__, __eq__, __lt__, __le__, etc.
-    assert BoringDataModule2(batch_size=32) is not None
+    assert BoringDataModule2(batch_size=32)
-    assert BoringDataModule2(batch_size=32).batch_size == 32
-    assert len(BoringDataModule2(batch_size=32)) == 0
     assert hasattr(BoringDataModule2, "__repr__")
     assert BoringDataModule2(batch_size=32).prepare_data() is None
     assert BoringDataModule2(batch_size=32) == BoringDataModule2(batch_size=32)
@@ -630,76 +625,3 @@ def test_inconsistent_prepare_data_per_node(tmpdir):
         trainer.model = model
         trainer.datamodule = dm
         trainer._data_connector.prepare_data()
-
-
-DATALOADER = DataLoader(RandomDataset(1, 32))
-
-
-@pytest.mark.parametrize("method_name", ["train_dataloader", "val_dataloader", "test_dataloader", "predict_dataloader"])
-@pytest.mark.parametrize(
-    ["dataloader", "expected"],
-    [
-        [DATALOADER, 32],
-        [[DATALOADER, DATALOADER], 64],
-        [[[DATALOADER], [DATALOADER, DATALOADER]], 96],
-        [[{"foo": DATALOADER}, {"foo": DATALOADER, "bar": DATALOADER}], 96],
-        [{"foo": DATALOADER, "bar": DATALOADER}, 64],
-        [{"foo": {"foo": DATALOADER}, "bar": {"foo": DATALOADER, "bar": DATALOADER}}, 96],
-        [{"foo": [DATALOADER], "bar": [DATALOADER, DATALOADER]}, 96],
-        [CombinedLoader({"foo": DATALOADER, "bar": DATALOADER}), 64],
-    ],
-)
-def test_len_different_types(method_name, dataloader, expected):
-    dm = LightningDataModule()
-    setattr(dm, method_name, lambda: dataloader)
-    assert len(dm) == expected
-
-
-@pytest.mark.parametrize("method_name", ["train_dataloader", "val_dataloader", "test_dataloader", "predict_dataloader"])
-def test_len_dataloader_no_len(method_name):
-    class CustomNotImplementedErrorDataloader(DataLoader):
-        def __len__(self):
-            raise NotImplementedError
-
-    dataloader = CustomNotImplementedErrorDataloader(RandomDataset(1, 32))
-    dm = LightningDataModule()
-    setattr(dm, method_name, lambda: dataloader)
-    with pytest.warns(UserWarning, match=f"The number of batches for a dataloader in `{method_name}` is counted as 0"):
-        assert len(dm) == 0
-
-
-def test_len_all_dataloader_methods_implemented():
-    class BoringDataModule(LightningDataModule):
-        def __init__(self, dataloader):
-            super().__init__()
-            self.dataloader = dataloader
-
-        def train_dataloader(self):
-            return {"foo": self.dataloader, "bar": self.dataloader}
-
-        def val_dataloader(self):
-            return self.dataloader
-
-        def test_dataloader(self):
-            return [self.dataloader]
-
-        def predict_dataloader(self):
-            return [self.dataloader, self.dataloader]
-
-    dm = BoringDataModule(DATALOADER)
-
-    # 6 dataloaders each producing 32 batches: 6 * 32 = 192
-    assert len(dm) == 192
-
-
-def test_len_no_dataloader_methods_implemented():
-    dm = LightningDataModule()
-    with pytest.warns(UserWarning, match="You datamodule does not have any valid dataloader"):
-        assert len(dm) == 0
-
-    dm.train_dataloader = None
-    dm.val_dataloader = None
-    dm.test_dataloader = None
-    dm.predict_dataloader = None
-    with pytest.warns(UserWarning, match="You datamodule does not have any valid dataloader"):
-        assert len(dm) == 0