bpo-43453: Update and re-add example to typing runtime_checkable (#27013)

akulakov · Fidget-Spinner · web-flow · commit 17f94e28882e · 2021-07-05T09:23:42.000-07:00
Co-authored-by: Ken Jin &lt;28750310+Fidget-Spinner@users.noreply.github.com&gt;
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
@@ -1232,8 +1232,13 @@ These are not used in annotations. They are building blocks for creating generic
 
    .. note::
 
-        :func:`runtime_checkable` will check only the presence of the required methods,
-        not their type signatures.
+        :func:`runtime_checkable` will check only the presence of the required
+        methods, not their type signatures. For example, :class:`ssl.SSLObject`
+        is a class, therefore it passes an :func:`issubclass`
+        check against :data:`Callable`.  However, the
+        :meth:`ssl.SSLObject.__init__` method exists only to raise a
+        :exc:`TypeError` with a more informative message, therefore making
+        it impossible to call (instantiate) :class:`ssl.SSLObject`.
 
    .. versionadded:: 3.8
 
