Issue #21481:  Teach argparse equality tests to return NotImplemented when comparing to unknown types.
diff --git a/Misc/NEWS b/Misc/NEWS
index 34c0074..663f389 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -21,6 +21,9 @@
 - Issue #8743: Fix interoperability between set objects and the
   collections.Set() abstract base class.
 
+- Issue #21481:  Argparse equality and inequality tests now return 
+  NotImplemented when comparing to an unknown type.
+
 Tests
 -----