Polishing --> code-block directive #3

Co-authored-by: Hong Xu <[email protected]>

index.rst

@@ -343,6 +343,8 @@ Additionally, it is possible to have ``indent_size`` less then the ``tab_width``
 
 To understand the way it works, let's look at the following example:
 
+.. code-block:: python
+
     def func():
         if True:
             return True