Fix data fetcher selection (#11294)

Author: awaelchli

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Fixed `LightningCLI` race condition while saving the config ([#11199](https://github.com/PyTorchLightning/pytorch-lightning/pull/11199))
 
+- Fixed data fetcher selection ([#11294](https://github.com/PyTorchLightning/pytorch-lightning/pull/11294))
 ## [1.5.7] - 2021-12-21
 
 ### Fixed

pytorch_lightning/trainer/connectors/data_connector.py

@@ -120,7 +120,7 @@ def _select_data_fetcher(self) -> AbstractDataFetcher:
 
     def get_profiled_dataloader(self, dataloader: Iterable, dataloader_idx: int = 0) -> Iterable:
         stage: str = self.trainer.state.stage.value
-        data_fetcher = setattr(self, f"{stage}_data_fetcher", None) or self._select_data_fetcher()
+        data_fetcher = getattr(self, f"{stage}_data_fetcher", None) or self._select_data_fetcher()
         data_fetcher.setup(
             dataloader,
             stage=stage,