LightningCLI support for argument links applied on instantiation

CHANGELOG.md

@@ -71,6 +71,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added a warning if `Trainer(log_every_n_steps)` is a value too high for the training dataloader ([#7734](https://github.com/PyTorchLightning/pytorch-lightning/pull/7734))
 
 
+- Added LightningCLI support for argument links applied on instantiation ([#7895](https://github.com/PyTorchLightning/pytorch-lightning/pull/7895))
+
+
 ### Changed
 
 - Changed calling of `untoggle_optimizer(opt_idx)` out of the closure function ([#7563](https://github.com/PyTorchLightning/pytorch-lightning/pull/7563)

docs/source/common/lightning_cli.rst

@@ -19,9 +19,13 @@
         ):
             pass
 
+    class MyClassModel(LightningModule):
+        def __init__(self, num_classes: int):
+            pass
+
     class MyDataModule(LightningDataModule):
         def __init__(self, batch_size: int = 8):
-            pass
+            self.num_classes = 5
 
     def send_email(address, message):
         pass
@@ -402,6 +406,22 @@ The linking of arguments is observed in the help of the tool, which for this exa
         model.batch_size <-- data.batch_size
                               Number of samples in a batch (type: int)
 
+Sometimes a parameter value is only available after class instantiation. An example could be that your model requires the number of classes to instantiate its fully connected layer (for a classification task) but the value is not available until the data module has been instantiated.
+The code below illustrates how to address this.
+
+.. testcode::
+
+    from pytorch_lightning.utilities.cli import LightningCLI
+
+    class MyLightningCLI(LightningCLI):
+
+        def add_arguments_to_parser(self, parser):
+            parser.link_arguments('data.num_classes', 'model.num_classes', apply_on='instantiate')
+
+    cli = MyLightningCLI(MyClassModel, MyDataModule)
+
+Instantiation links are used to automatically determine the order of instantiation, in this case data first.
+
 .. tip::
 
     The linking of arguments can be used for more complex cases. For example to derive a value via a function that takes

pytorch_lightning/utilities/cli.py

@@ -66,7 +66,12 @@ def add_lightning_class_args(
         assert issubclass(lightning_class, (Trainer, LightningModule, LightningDataModule))
         if subclass_mode:
             return self.add_subclass_arguments(lightning_class, nested_key, required=True)
-        return self.add_class_arguments(lightning_class, nested_key, fail_untyped=False)
+        return self.add_class_arguments(
+            lightning_class,
+            nested_key,
+            fail_untyped=False,
+            instantiate=not issubclass(lightning_class, Trainer),
+        )
 
 
 class SaveConfigCallback(Callback):
@@ -212,27 +217,11 @@ def before_instantiate_classes(self) -> None:
 
     def instantiate_classes(self) -> None:
         """Instantiates the classes using settings from self.config"""
-        self.config_init = self.parser.instantiate_subclasses(self.config)
-        self.instantiate_datamodule()
-        self.instantiate_model()
+        self.config_init = self.parser.instantiate_classes(self.config)
+        self.datamodule = self.config_init.get('data')
+        self.model = self.config_init['model']
         self.instantiate_trainer()
 
-    def instantiate_datamodule(self) -> None:
-        """Instantiates the datamodule using self.config_init['data'] if given"""
-        if self.datamodule_class is None:
-            self.datamodule = None
-        elif self.subclass_mode_data:
-            self.datamodule = self.config_init['data']
-        else:
-            self.datamodule = self.datamodule_class(**self.config_init.get('data', {}))
-
-    def instantiate_model(self) -> None:
-        """Instantiates the model using self.config_init['model']"""
-        if self.subclass_mode_model:
-            self.model = self.config_init['model']
-        else:
-            self.model = self.model_class(**self.config_init.get('model', {}))
-
     def instantiate_trainer(self) -> None:
         """Instantiates the trainer using self.config_init['trainer']"""
         if self.config_init['trainer'].get('callbacks') is None:

requirements/extra.txt

@@ -7,4 +7,4 @@ torchtext>=0.5
 # onnx>=1.7.0
 onnxruntime>=1.3.0
 hydra-core>=1.0
-jsonargparse[signatures]>=3.13.1
+jsonargparse[signatures]>=3.14.0

tests/utilities/test_cli.py

@@ -446,11 +446,9 @@ def __init__(
     with mock.patch('sys.argv', ['any.py'] + cli_args):
         cli = LightningCLI(MainModule)
 
-    assert cli.config_init['model']['main_param'] == 2
-    assert cli.model.submodule1 == cli.config_init['model']['submodule1']
-    assert cli.model.submodule2 == cli.config_init['model']['submodule2']
-    assert isinstance(cli.config_init['model']['submodule1'], BoringModel)
-    assert isinstance(cli.config_init['model']['submodule2'], BoringModel)
+    assert cli.config['model']['main_param'] == 2
+    assert isinstance(cli.model.submodule1, BoringModel)
+    assert isinstance(cli.model.submodule2, BoringModel)
 
 
 @pytest.mark.skipif(torchvision_version < version.parse('0.8.0'), reason='torchvision>=0.8.0 is required')
@@ -497,3 +495,65 @@ def __init__(
     assert cli.model.activation.negative_slope == 0.2
     assert len(cli.model.transform) == 2
     assert all(isinstance(v, torch.nn.Module) for v in cli.model.transform)
+
+
+class BoringModelRequiredClasses(BoringModel):
+
+    def __init__(
+        self,
+        num_classes: int,
+        batch_size: int = 8,
+    ):
+        super().__init__()
+        self.num_classes = num_classes
+        self.batch_size = batch_size
+
+
+class BoringDataModuleBatchSizeAndClasses(BoringDataModule):
+
+    def __init__(
+        self,
+        batch_size: int = 8,
+    ):
+        super().__init__()
+        self.batch_size = batch_size
+        self.num_classes = 5  # only available after instantiation
+
+
+def test_lightning_cli_link_arguments(tmpdir):
+
+    class MyLightningCLI(LightningCLI):
+
+        def add_arguments_to_parser(self, parser):
+            parser.link_arguments('data.batch_size', 'model.batch_size')
+            parser.link_arguments('data.num_classes', 'model.num_classes', apply_on='instantiate')
+
+    cli_args = [
+        f'--trainer.default_root_dir={tmpdir}',
+        '--trainer.max_epochs=1',
+        '--data.batch_size=12',
+    ]
+
+    with mock.patch('sys.argv', ['any.py'] + cli_args):
+        cli = MyLightningCLI(BoringModelRequiredClasses, BoringDataModuleBatchSizeAndClasses)
+
+    assert cli.model.batch_size == 12
+    assert cli.model.num_classes == 5
+
+    class MyLightningCLI(LightningCLI):
+
+        def add_arguments_to_parser(self, parser):
+            parser.link_arguments('data.batch_size', 'model.init_args.batch_size')
+            parser.link_arguments('data.num_classes', 'model.init_args.num_classes', apply_on='instantiate')
+
+    cli_args[-1] = '--model=tests.utilities.test_cli.BoringModelRequiredClasses'
+
+    with mock.patch('sys.argv', ['any.py'] + cli_args):
+        cli = MyLightningCLI(
+            BoringModelRequiredClasses,
+            BoringDataModuleBatchSizeAndClasses,
+            subclass_mode_model=True,
+        )
+
+    assert cli.model.batch_size == 8
+    assert cli.model.num_classes == 5