add proper deprecation

pytorch_lightning/trainer/deprecated_api.py

@@ -11,6 +11,7 @@
 # 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 pytorch_lightning.core.lightning import LightningModule
 from pytorch_lightning.trainer.connectors.accelerator_connector import AcceleratorConnector
 from pytorch_lightning.trainer.states import RunningStage
 from pytorch_lightning.utilities import DeviceType, DistributedType, rank_zero_warn
@@ -23,6 +24,7 @@ class DeprecatedDistDeviceAttributes:
     _running_stage: RunningStage
     num_gpus: int
     accelerator_connector: AcceleratorConnector
+    lightning_module = LightningModule
 
     @property
     def on_cpu(self) -> bool:
@@ -130,3 +132,11 @@ def use_single_gpu(self, val: bool) -> None:
         )
         if val:
             self.accelerator_connector._device_type = DeviceType.GPU
+
+    def get_model(self) -> LightningModule:
+        rank_zero_warn(
+            "The use of `Trainer.get_model()` is deprecated in favor of `Trainer.lightning_module`"
+            " and will be removed in v1.4.",
+            DeprecationWarning,
+        )
+        return self.lightning_module

pytorch_lightning/trainer/properties.py

@@ -352,10 +352,6 @@ def model(self, model: torch.nn.Module) -> None:
         """
         self.accelerator.model = model
 
-    def get_model(self) -> LightningModule:
-        # backward compatible
-        return self.lightning_module
-
     @property
     def lightning_optimizers(self) -> List[LightningOptimizer]:
         if self._lightning_optimizers is None:

tests/deprecated_api/test_remove_1-4.py

@@ -30,6 +30,13 @@
 from tests.helpers import BoringModel
 
 
+def test_v1_4_0_deprecated_trainer_methods():
+    with pytest.deprecated_call(match='will be removed in v1.4'):
+        trainer = Trainer()
+        _ = trainer.get_model()
+    assert trainer.get_model() == trainer.lightning_module
+
+
 def test_v1_4_0_deprecated_imports():
     _soft_unimport_module('pytorch_lightning.utilities.argparse_utils')
     with pytest.deprecated_call(match='will be removed in v1.4'):