Fix mypy errors attributed to `pytorch_lightning.core.mixins.device_dtype_mixin` (#13704)

Co-authored-by: Adrian Wälchli <aedu.waelchli@gmail.com>

pyproject.toml

@@ -52,7 +52,6 @@ module = [
     "pytorch_lightning.callbacks.stochastic_weight_avg",
     "pytorch_lightning.core.datamodule",
     "pytorch_lightning.core.decorators",
-    "pytorch_lightning.core.mixins.device_dtype_mixin",
     "pytorch_lightning.core.module",
     "pytorch_lightning.core.saving",
     "pytorch_lightning.demos.boring_classes",

src/pytorch_lightning/core/mixins/device_dtype_mixin.py

@@ -16,16 +16,7 @@ from typing import Any, Optional, Union
 
 import torch
 from torch.nn import Module
-
-try:
-    from typing_extensions import Self
-except ImportError:
-    # workaround for Python 3.7.
-    # see https://www.python.org/dev/peps/pep-0673/
-    from typing import TypeVar
-
-    Self = TypeVar("TDeviceDtypeModuleMixin", bound="DeviceDtypeModuleMixin")
-
+from typing_extensions import Self
 
 import pytorch_lightning as pl
 
@@ -57,7 +48,7 @@ class DeviceDtypeModuleMixin(Module):
 
         return device
 
-    def to(self, *args: Any, **kwargs: Any) -> Self:
+    def to(self, *args: Any, **kwargs: Any) -> Self:  # type: ignore[valid-type]
         """Moves and/or casts the parameters and buffers.
 
         This can be called as
@@ -121,7 +112,7 @@ class DeviceDtypeModuleMixin(Module):
         self.__update_properties(device=out[0], dtype=out[1])
         return super().to(*args, **kwargs)
 
-    def cuda(self, device: Optional[Union[torch.device, int]] = None) -> Self:
+    def cuda(self, device: Optional[Union[torch.device, int]] = None) -> Self:  # type: ignore[valid-type]
         """Moves all model parameters and buffers to the GPU. This also makes associated parameters and buffers
         different objects. So it should be called before constructing optimizer if the module will live on GPU
         while being optimized.
@@ -134,11 +125,11 @@ class DeviceDtypeModuleMixin(Module):
             Module: self
         """
         if device is None or isinstance(device, int):
-            device = torch.device("cuda", index=device)
+            device = torch.device("cuda", index=(device or 0))
         self.__update_properties(device=device)
         return super().cuda(device=device)
 
-    def cpu(self) -> Self:
+    def cpu(self) -> Self:  # type: ignore[valid-type]
         """Moves all model parameters and buffers to the CPU.
 
         Returns:
@@ -147,7 +138,7 @@ class DeviceDtypeModuleMixin(Module):
         self.__update_properties(device=torch.device("cpu"))
         return super().cpu()
 
-    def type(self, dst_type: Union[str, torch.dtype]) -> Self:
+    def type(self, dst_type: Union[str, torch.dtype]) -> Self:  # type: ignore[valid-type]
         """Casts all parameters and buffers to :attr:`dst_type`.
 
         Arguments:
@@ -159,7 +150,7 @@ class DeviceDtypeModuleMixin(Module):
         self.__update_properties(dtype=dst_type)
         return super().type(dst_type=dst_type)
 
-    def float(self) -> Self:
+    def float(self) -> Self:  # type: ignore[valid-type]
         """Casts all floating point parameters and buffers to ``float`` datatype.
 
         Returns:
@@ -168,7 +159,7 @@ class DeviceDtypeModuleMixin(Module):
         self.__update_properties(dtype=torch.float)
         return super().float()
 
-    def double(self) -> Self:
+    def double(self) -> Self:  # type: ignore[valid-type]
         """Casts all floating point parameters and buffers to ``double`` datatype.
 
         Returns:
@@ -177,7 +168,7 @@ class DeviceDtypeModuleMixin(Module):
         self.__update_properties(dtype=torch.double)
         return super().double()
 
-    def half(self) -> Self:
+    def half(self) -> Self:  # type: ignore[valid-type]
         """Casts all floating point parameters and buffers to ``half`` datatype.
 
         Returns: