Support strategy argument being case insensitive

CHANGELOG.md

@@ -25,7 +25,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Changed
 
--
+- Support `strategy` argument being case insensitive ([#12528](https://github.com/PyTorchLightning/pytorch-lightning/pull/12528))
 
 
 -

pytorch_lightning/trainer/connectors/accelerator_connector.py

@@ -244,6 +244,9 @@ def _check_config_and_set_final_flags(
         if plugins is not None:
             plugins = [plugins] if not isinstance(plugins, list) else plugins
 
+        if isinstance(strategy, str):
+            strategy = strategy.lower()
+
         if strategy is not None:
             self._strategy_flag = strategy
             if strategy == "ddp_cpu":

tests/strategies/test_common.py

@@ -16,6 +16,7 @@
 
 import tests.helpers.utils as tutils
 from pytorch_lightning import Trainer
+from pytorch_lightning.strategies import DDPStrategy
 from pytorch_lightning.utilities.seed import seed_everything
 from tests.helpers.boring_model import BoringModel
 from tests.helpers.datamodules import ClassifDataModule
@@ -69,3 +70,12 @@ def configure_sharded_model(self):
     trainer.fit(model)
 
     assert model.configure_sharded_model_called
+
+
+@pytest.mark.parametrize(
+    ["strategy", "strategy_cls"], [("DDP", DDPStrategy), ("DDP_FIND_UNUSED_PARAMETERS_FALSE", DDPStrategy)]
+)
+def test_strategy_str_passed_being_case_insensitive(strategy, strategy_cls):
+
+    trainer = Trainer(strategy=strategy)
+    assert isinstance(trainer.strategy, strategy_cls)