Fix method stub used for fixing mypy issue to work with pylint (pytor…

…ch#42356)

Summary:
Make function from method

Since _forward_unimplemented is defined within the nn.Module class,
pylint (correctly) complains about not implementing this method in subclasses.

Fixes pytorch#42305

Pull Request resolved: pytorch#42356

Reviewed By: mruberry

Differential Revision: D22867255

Pulled By: ezyang

fbshipit-source-id: ccf3e45e359d927e010791fadf70b2ef231ddb0b

torch/nn/modules/module.py

@@ -158,6 +158,13 @@ def register_module_backward_hook(
     return handle
 
 
+# Trick mypy into not applying contravariance rules to inputs by defining
+# forward as a value, rather than a function.  See also
+# https://github.com/python/mypy/issues/8795
+def _forward_unimplemented(self, *input: Any) -> None:
+    raise NotImplementedError
+
+
 class Module:
     r"""Base class for all neural network modules.
 
@@ -220,12 +227,6 @@ def __init__(self):
         self._load_state_dict_pre_hooks = OrderedDict()
         self._modules = OrderedDict()
 
-    # Trick mypy into not applying contravariance rules to inputs by defining
-    # forward as a value, rather than a function.  See also
-    # https://github.com/python/mypy/issues/8795
-    def _forward_unimplemented(self, *input: Any) -> None:
-        raise NotImplementedError
-
     r"""Defines the computation performed at every call.
 
     Should be overridden by all subclasses.