Make get_type_hints not throw an error on builtin methods (#368)

* Added support to get_type_hints for builtin methods like object.__init__ or object.__str__ etc.

* Fixed tabs vs spaces -.-

* Changed the type check for builtin functions/methods to use the new types in the types module.

Author: wheerd

src/test_typing.py

@@ -1542,12 +1542,15 @@ def meth(x: int): ...
         class Der(ABase): ...
         self.assertEqual(gth(ABase.meth), {'x': int})
 
-    def test_get_type_hints_for_builins(self):
+    def test_get_type_hints_for_builtins(self):
         # Should not fail for built-in classes and functions.
         self.assertEqual(gth(int), {})
         self.assertEqual(gth(type), {})
         self.assertEqual(gth(dir), {})
         self.assertEqual(gth(len), {})
+        self.assertEqual(gth(object.__str__), {})
+        self.assertEqual(gth(object().__str__), {})
+        self.assertEqual(gth(str.join), {})
 
     def test_previous_behavior(self):
         def testf(x, y): ...

src/typing.py

@@ -10,6 +10,12 @@
     import collections.abc as collections_abc
 except ImportError:
     import collections as collections_abc  # Fallback for PY3.2.
+try:
+    from types import SlotWrapperType, MethodWrapperType, MethodDescriptorType
+except ImportError:
+    SlotWrapperType = type(object.__init__)
+    MethodWrapperType = type(object().__str__)
+    MethodDescriptorType = type(str.join)
 
 
 # Please keep __all__ alphabetized within each category.
@@ -1459,7 +1465,10 @@ def get_type_hints(obj, globalns=None, localns=None):
             isinstance(obj, types.FunctionType) or
             isinstance(obj, types.BuiltinFunctionType) or
             isinstance(obj, types.MethodType) or
-            isinstance(obj, types.ModuleType)
+            isinstance(obj, types.ModuleType) or
+            isinstance(obj, SlotWrapperType) or
+            isinstance(obj, MethodWrapperType) or
+            isinstance(obj, MethodDescriptorType)
         ):
             return {}
         else: