Issue #9214: Fix set operations on KeysView and ItemsView.

Lib/_abcoll.py

@@ -390,6 +390,10 @@ class MappingView(Sized):
 
 class KeysView(MappingView, Set):
 
+    @classmethod
+    def _from_iterable(self, it):
+        return set(it)
+
     def __contains__(self, key):
         return key in self._mapping
 
@@ -400,6 +404,10 @@ class KeysView(MappingView, Set):
 
 class ItemsView(MappingView, Set):
 
+    @classmethod
+    def _from_iterable(self, it):
+        return set(it)
+
     def __contains__(self, item):
         key, value = item
         try:

Misc/NEWS

@@ -31,6 +31,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #9214: Set operations on KeysView or ItemsView in the collections
+  module now correctly return a set.  (Patch by Eli Bendersky.)
+
 - Issue #9617: Signals received during a low-level write operation aren't
   ignored by the buffered IO layer anymore.