Lite: Support self.log from a LightningModule

src/lightning_fabric/CHANGELOG.md

@@ -35,7 +35,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
   * Added `Fabric.log` for logging scalars using multiple loggers
   * Added `Fabric.log_dict` for logging a dictionary of multiple metrics at once
   * Added `Fabric.loggers` and `Fabric.logger` attributes to access the individual logger instances
-
+  * Added support for calling `self.log` and `self.log_dict` in a LightningModule when using Fabric
+  * Added access to `self.logger` and `self.loggers` in a LightningModule when using Fabric
 
 - Added support for a consistent `.zero_grad(set_to_none=...)` on the wrapped optimizer regardless of which strategy is used ([#16275](https://github.com/Lightning-AI/lightning/issues/16275))
 

src/lightning_fabric/fabric.py

@@ -597,7 +597,8 @@ def log(self, name: str, value: Any, step: Optional[int] = None) -> None:
 
         Args:
             name: The name of the metric to log.
-            value: The metric value to collect.
+            value: The metric value to collect. If the value is a :class:`torch.Tensor`, it gets detached from the
+                graph automatically.
             step: Optional step number. Most Logger implementations auto-increment the step value by one with every
                 log call. You can specify your own value here.
         """
@@ -608,9 +609,17 @@ def log_dict(self, metrics: Dict[str, Any], step: Optional[int] = None) -> None:
 
         Args:
             metrics: A dictionary where the key is the name of the metric and the value the scalar to be logged.
+                Any :class:`torch.Tensor`s in the dictionary get detached from the graph automatically.
             step: Optional step number. Most Logger implementations auto-increment this value by one with every
                 log call. You can specify your own value here.
         """
+
+        def to_item(value: Tensor) -> Union[int, float, bool]:
+            if value.numel() != 1:
+                raise ValueError("Logging tensors with more than one element is not supported.")
+            return value.item()
+
+        metrics = apply_to_collection(metrics, dtype=Tensor, function=to_item)
         for logger in self._loggers:
             logger.log_metrics(metrics=metrics, step=step)
 

src/lightning_fabric/utilities/apply_func.py

@@ -111,3 +111,21 @@ def _move_to_device_and_make_contiguous(t: Tensor, device: _DEVICE) -> Tensor:
 
     # make sure existing tensors are in the correct device, also contiguous
     return apply_to_collection(data, Tensor, _move_to_device_and_make_contiguous, device=device)
+
+
+def convert_tensors_to_scalars(data: Any) -> Any:
+    """Recursively walk through a collection and convert single-item tensors to scalar values.
+
+    Raises:
+        ValueError:
+            If tensors inside ``metrics`` contains multiple elements, hence preventing conversion to a scalar.
+    """
+
+    def to_item(value: Tensor) -> Union[int | float | bool]:
+        if value.numel() != 1:
+            raise ValueError(
+                f"The metric `{value}` does not contain a single element, thus it cannot be converted to a scalar."
+            )
+        return value.item()
+
+    return apply_to_collection(data, Tensor, to_item)

src/pytorch_lightning/core/module.py

@@ -403,6 +403,10 @@ def log(
             rank_zero_only: Whether the value will be logged only on rank 0. This will prevent synchronization which
                 would produce a deadlock as not all processes would perform this log call.
         """
+        if self._fabric is not None:
+            self._log_dict_through_fabric(dictionary={name: value}, logger=logger)
+            return
+
         # check for invalid values
         apply_to_collection(value, dict, self.__check_not_nested, name)
         apply_to_collection(
@@ -554,22 +558,39 @@ def log_dict(
             rank_zero_only: Whether the value will be logged only on rank 0. This will prevent synchronization which
                 would produce a deadlock as not all processes would perform this log call.
         """
-        for k, v in dictionary.items():
-            self.log(
-                name=k,
-                value=v,
-                prog_bar=prog_bar,
-                logger=logger,
-                on_step=on_step,
-                on_epoch=on_epoch,
-                reduce_fx=reduce_fx,
-                enable_graph=enable_graph,
-                sync_dist=sync_dist,
-                sync_dist_group=sync_dist_group,
-                add_dataloader_idx=add_dataloader_idx,
-                batch_size=batch_size,
-                rank_zero_only=rank_zero_only,
-            )
+        if self._fabric is not None:
+            self._log_dict_through_fabric(dictionary=dictionary, logger=logger)  # type: ignore[arg-type]
+        else:
+            for k, v in dictionary.items():
+                self.log(
+                    name=k,
+                    value=v,
+                    prog_bar=prog_bar,
+                    logger=logger,
+                    on_step=on_step,
+                    on_epoch=on_epoch,
+                    reduce_fx=reduce_fx,
+                    enable_graph=enable_graph,
+                    sync_dist=sync_dist,
+                    sync_dist_group=sync_dist_group,
+                    add_dataloader_idx=add_dataloader_idx,
+                    batch_size=batch_size,
+                    rank_zero_only=rank_zero_only,
+                )
+
+    def _log_dict_through_fabric(self, dictionary: Dict[str, Any], logger: Optional[bool] = None) -> None:
+        if logger is False:
+            # Passing `logger=False` with Fabric does not make much sense because there is no other destination to
+            # log to, but we support it in case the original code was written for Trainer use
+            return
+
+        if any(isinstance(v, dict) for v in dictionary.values()):
+            raise ValueError(f"`self.log_dict({dictionary})` was called, but nested dictionaries cannot be logged")
+        for name, value in dictionary.items():
+            apply_to_collection(value, object, self.__check_allowed, name, value, wrong_dtype=(numbers.Number, Tensor))
+
+        assert self._fabric is not None
+        self._fabric.log_dict(metrics=dictionary)
 
     @staticmethod
     def __check_not_nested(value: dict, name: str) -> None:

src/pytorch_lightning/trainer/connectors/logger_connector/logger_connector.py

@@ -19,9 +19,9 @@
 import pytorch_lightning as pl
 from lightning_fabric.plugins.environments import SLURMEnvironment
 from lightning_fabric.utilities import move_data_to_device
+from lightning_fabric.utilities.apply_func import convert_tensors_to_scalars
 from pytorch_lightning.loggers import Logger, TensorBoardLogger
 from pytorch_lightning.trainer.connectors.logger_connector.result import _METRICS, _OUT_DICT, _PBAR_DICT
-from pytorch_lightning.utilities.metrics import metrics_to_scalars
 
 
 class LoggerConnector:
@@ -80,7 +80,7 @@ def log_metrics(self, metrics: _OUT_DICT, step: Optional[int] = None) -> None:
         self._logged_metrics.update(metrics)
 
         # turn all tensors to scalars
-        scalar_metrics = metrics_to_scalars(metrics)
+        scalar_metrics = convert_tensors_to_scalars(metrics)
 
         if step is None:
             step = scalar_metrics.pop("step", None)

src/pytorch_lightning/trainer/connectors/logger_connector/result.py

@@ -22,13 +22,13 @@
 from typing_extensions import TypedDict
 
 from lightning_fabric.utilities import move_data_to_device
+from lightning_fabric.utilities.apply_func import convert_tensors_to_scalars
 from lightning_fabric.utilities.device_dtype_mixin import _DeviceDtypeModuleMixin
 from lightning_fabric.utilities.distributed import _distributed_available
 from pytorch_lightning.utilities.data import extract_batch_size
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.imports import _fault_tolerant_training
 from pytorch_lightning.utilities.memory import recursive_detach
-from pytorch_lightning.utilities.metrics import metrics_to_scalars
 from pytorch_lightning.utilities.rank_zero import rank_zero_warn, WarningCache
 from pytorch_lightning.utilities.warnings import PossibleUserWarning
 
@@ -610,7 +610,7 @@ def any_tensor(_: Any) -> None:
 
             # populate progress_bar metrics. convert tensors to numbers
             if result_metric.meta.prog_bar:
-                metrics["pbar"][forked_name] = metrics_to_scalars(value)
+                metrics["pbar"][forked_name] = convert_tensors_to_scalars(value)
 
         return metrics
 

src/pytorch_lightning/utilities/metrics.py

@@ -12,29 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 """Helper functions to operate on metric values."""
-from __future__ import annotations
 
 from typing import Any
 
-from lightning_utilities.core.apply_func import apply_to_collection
-from torch import Tensor
-
-from pytorch_lightning.utilities.exceptions import MisconfigurationException
+from lightning_fabric.utilities.apply_func import convert_tensors_to_scalars
 
 
 def metrics_to_scalars(metrics: Any) -> Any:
     """Recursively walk through a collection and convert single-item tensors to scalar values.
 
     Raises:
-        MisconfigurationException:
+        ValueError:
             If tensors inside ``metrics`` contains multiple elements, hence preventing conversion to a scalar.
     """
 
-    def to_item(value: Tensor) -> int | float | bool:
-        if value.numel() != 1:
-            raise MisconfigurationException(
-                f"The metric `{value}` does not contain a single element, thus it cannot be converted to a scalar."
-            )
-        return value.item()
-
-    return apply_to_collection(metrics, Tensor, to_item)
+    return convert_tensors_to_scalars(metrics)

tests/tests_fabric/test_fabric.py

@@ -800,3 +800,28 @@ def test_log_dict():
     fabric.log_dict({"foo": 3, "bar": 4}, step=15)
     logger0.log_metrics.assert_called_with(metrics={"foo": 3, "bar": 4}, step=15)
     logger1.log_metrics.assert_called_with(metrics={"foo": 3, "bar": 4}, step=15)
+
+
+def test_log_dict_input_parsing():
+    """Test validation of input data types and preprocessing."""
+    logger = Mock()
+    fabric = Fabric(loggers=[logger])
+
+    # Tensor scalar, 0 dims
+    fabric.log("log", torch.tensor(1))
+    logger.log_metrics.assert_called_with(metrics={"log": 1}, step=None)
+    fabric.log_dict({"log_dict": torch.tensor(1)})
+    logger.log_metrics.assert_called_with(metrics={"log_dict": 1}, step=None)
+
+    # Tensor scalar, 1 dims
+    fabric.log("log", torch.tensor([2]))
+    logger.log_metrics.assert_called_with(metrics={"log": 2}, step=None)
+    fabric.log_dict({"log_dict": torch.tensor([2])})
+    logger.log_metrics.assert_called_with(metrics={"log_dict": 2}, step=None)
+
+    # Tensor, multiple dims
+    with pytest.raises(ValueError, match="Logging tensors with more than one element is not supported"):
+        fabric.log("log", torch.tensor([3, 4]))
+
+    with pytest.raises(ValueError, match="Logging tensors with more than one element is not supported"):
+        fabric.log_dict({"log_dict": torch.tensor([3, 4])})

tests/tests_pytorch/core/test_lightning_module.py

@@ -512,13 +512,89 @@ def test_fabric_attributes():
 
     fabric = Fabric()
     wrapped_module, wrapped_optimizer = fabric.setup(module, optimizer)
-    assert module.fabric is fabric
-    assert module._fabric_optimizers == [wrapped_optimizer]
+    assert wrapped_module.fabric is fabric
+    assert wrapped_module._fabric_optimizers == [wrapped_optimizer]
 
     # Attribute access on LightningModule.trainer gets redirected to Fabric
-    assert isinstance(module.trainer, _TrainerFabricShim)
-    assert module.trainer.global_rank == 0
+    assert isinstance(wrapped_module.trainer, _TrainerFabricShim)
+    assert wrapped_module.trainer.global_rank == 0
     with pytest.raises(AttributeError, match="Your LightningModule code tried to access `self.trainer.current_epoch`"):
-        _ = module.trainer.current_epoch
+        _ = wrapped_module.trainer.current_epoch
 
-    assert module.optimizers() == wrapped_optimizer
+    assert wrapped_module.optimizers() == wrapped_optimizer
+
+
+def test_fabric_logger_access():
+    """Test that the logger attribute can be accessed when the LightningModule is used together with Fabric."""
+    # No logger
+    module = BoringModel()
+    fabric = Fabric()
+    wrapped_module = fabric.setup(module)
+    assert wrapped_module.loggers == []
+    with pytest.raises(IndexError):
+        _ = wrapped_module.logger
+
+    # Single Logger
+    logger = Mock()
+    module = BoringModel()
+    fabric = Fabric(loggers=logger)
+    wrapped_module = fabric.setup(module)
+    assert wrapped_module.logger == logger
+    assert wrapped_module.loggers == [logger]
+
+    # Multiple loggers
+    logger1 = Mock()
+    logger2 = Mock()
+    module = BoringModel()
+    fabric = Fabric(loggers=[logger1, logger2])
+    wrapped_module = fabric.setup(module)
+    assert wrapped_module.logger == logger1
+    assert wrapped_module.loggers == [logger1, logger2]
+
+
+def test_fabric_log():
+    logger = Mock()
+    module = BoringModel()
+    fabric = Fabric(loggers=[logger])
+    wrapped_module = fabric.setup(module)
+
+    # unsupported data type
+    with pytest.raises(ValueError, match="`list` values cannot be logged"):
+        wrapped_module.log("invalid", list())
+
+    # supported data types
+    wrapped_module.log("int", 1)
+    logger.log_metrics.assert_called_with(metrics={"int": 1}, step=None)
+    wrapped_module.log("float", 0.1)
+    logger.log_metrics.assert_called_with(metrics={"float": 0.1}, step=None)
+    wrapped_module.log("tensor", torch.tensor(0.1))
+    logger.log_metrics.assert_called_with(metrics={"tensor": torch.tensor(0.1)}, step=None)
+
+    # logger=False
+    logger.reset_mock()
+    wrapped_module.log("nothing", 1, logger=False)
+    logger.log_metrics.assert_not_called()
+
+
+def test_fabric_log_dict():
+    logger = Mock()
+    module = BoringModel()
+    fabric = Fabric(loggers=[logger])
+    wrapped_module = fabric.setup(module)
+
+    # unsupported data type
+    with pytest.raises(ValueError, match="`list` values cannot be logged"):
+        wrapped_module.log_dict({"invalid": [1, 2, 3]})
+
+    # nested dicts
+    with pytest.raises(ValueError, match="nested dictionaries cannot be logged"):
+        wrapped_module.log_dict({"nested": {"nested": 1}})
+
+    # supported data types
+    wrapped_module.log_dict({"int": 1, "float": 0.1, "tensor": torch.tensor(0.1)})
+    logger.log_metrics.assert_called_with(metrics={"int": 1, "float": 0.1, "tensor": torch.tensor(0.1)}, step=None)
+
+    # logger=False
+    logger.reset_mock()
+    wrapped_module.log_dict({"nothing": 1}, logger=False)
+    logger.log_metrics.assert_not_called()