Issue #13557: Clarify effect of giving two different namespaces to exec or

execfile().

Doc/library/functions.rst

@@ -430,7 +430,10 @@ available.  They are listed here in alphabetical order.
    The arguments are a file name and two optional dictionaries.  The file is parsed
    and evaluated as a sequence of Python statements (similarly to a module) using
    the *globals* and *locals* dictionaries as global and local namespace. If
-   provided, *locals* can be any mapping object.
+   provided, *locals* can be any mapping object.  Remember that at module level,
+   globals and locals are the same dictionary. If two separate objects are
+   passed as *globals* and *locals*, the code will be executed as if it were
+   embedded in a class definition.
 
    .. versionchanged:: 2.4
       formerly *locals* was required to be a dictionary.

Doc/reference/simple_stmts.rst

@@ -993,6 +993,9 @@ current scope.  If only the first expression after :keyword:`in` is specified,
 it should be a dictionary, which will be used for both the global and the local
 variables.  If two expressions are given, they are used for the global and local
 variables, respectively. If provided, *locals* can be any mapping object.
+Remember that at module level, globals and locals are the same dictionary. If
+two separate objects are given as *globals* and *locals*, the code will be
+executed as if it were embedded in a class definition.
 
 .. versionchanged:: 2.4
    Formerly, *locals* was required to be a dictionary.

Misc/NEWS

@@ -284,7 +284,9 @@ Build
 - Issue #14437: Fix building the _io module under Cygwin.
 
 Documentation
--------------
+
+- Issue #13557: Clarify effect of giving two different namespaces to exec or
+  execfile().
 
 - Issue #14034: added the argparse tutorial.