Replaced .keys() with dictionary iterators
diff --git a/Lib/inspect.py b/Lib/inspect.py
index e40ec8d..fdbe16a 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -553,7 +553,7 @@
                 if unique and parent in classes: break
         elif c not in roots:
             roots.append(c)
-    for parent in children.keys():
+    for parent in children:
         if parent not in classes:
             roots.append(parent)
     return walktree(roots, children, None)