#5991: let completion for the "help" command include help topics.

This also simplifies the Cmd.get_names() method implementation; it was written
at a time where dir() didn't consider base class attributes.

Lib/cmd.py

@@ -281,19 +281,15 @@ class Cmd:
             return None
 
     def get_names(self):
-        # Inheritance says we have to look in class and
-        # base classes; order is not important.
-        names = []
-        classes = [self.__class__]
-        while classes:
-            aclass = classes.pop(0)
-            if aclass.__bases__:
-                classes = classes + list(aclass.__bases__)
-            names = names + dir(aclass)
-        return names
+        # This method used to pull in base class attributes
+        # at a time dir() didn't do it yet.
+        return dir(self.__class__)
 
     def complete_help(self, *args):
-        return self.completenames(*args)
+        commands = set(self.completenames(*args))
+        topics = set(a[5:] for a in self.get_names()
+                     if a.startswith('help_' + args[0]))
+        return list(commands | topics)
 
     def do_help(self, arg):
         if arg: