Remove List[int] as input type for Trainer when accelerator="cpu" (…

…#20399)

Co-authored-by: Alan Chu <[email protected]>
Co-authored-by: Jirka Borovec <[email protected]>

src/lightning/fabric/accelerators/cpu.py

@@ -39,13 +39,13 @@ def teardown(self) -> None:
 
     @staticmethod
     @override
-    def parse_devices(devices: Union[int, str, List[int]]) -> int:
+    def parse_devices(devices: Union[int, str]) -> int:
         """Accelerator device parsing logic."""
         return _parse_cpu_cores(devices)
 
     @staticmethod
     @override
-    def get_parallel_devices(devices: Union[int, str, List[int]]) -> List[torch.device]:
+    def get_parallel_devices(devices: Union[int, str]) -> List[torch.device]:
         """Gets parallel devices for the Accelerator."""
         devices = _parse_cpu_cores(devices)
         return [torch.device("cpu")] * devices
@@ -72,12 +72,12 @@ def register_accelerators(cls, accelerator_registry: _AcceleratorRegistry) -> No
         )
 
 
-def _parse_cpu_cores(cpu_cores: Union[int, str, List[int]]) -> int:
+def _parse_cpu_cores(cpu_cores: Union[int, str]) -> int:
     """Parses the cpu_cores given in the format as accepted by the ``devices`` argument in the
     :class:`~lightning.pytorch.trainer.trainer.Trainer`.
 
     Args:
-        cpu_cores: An int > 0.
+        cpu_cores: An int > 0 or a string that can be converted to an int > 0.
 
     Returns:
         An int representing the number of processes

src/lightning/pytorch/accelerators/cpu.py

@@ -48,13 +48,13 @@ def teardown(self) -> None:
 
     @staticmethod
     @override
-    def parse_devices(devices: Union[int, str, List[int]]) -> int:
+    def parse_devices(devices: Union[int, str]) -> int:
         """Accelerator device parsing logic."""
         return _parse_cpu_cores(devices)
 
     @staticmethod
     @override
-    def get_parallel_devices(devices: Union[int, str, List[int]]) -> List[torch.device]:
+    def get_parallel_devices(devices: Union[int, str]) -> List[torch.device]:
         """Gets parallel devices for the Accelerator."""
         devices = _parse_cpu_cores(devices)
         return [torch.device("cpu")] * devices