bpo-37646: Document that eval() cannot access nested scopes (GH-15117)

Doc/library/functions.rst

@@ -465,12 +465,16 @@ are always available.  They are listed here in alphabetical order.
    dictionaries as global and local namespace.  If the *globals* dictionary is
    present and does not contain a value for the key ``__builtins__``, a
    reference to the dictionary of the built-in module :mod:`builtins` is
-   inserted under that key before *expression* is parsed.
-   This means that *expression* normally has full
-   access to the standard :mod:`builtins` module and restricted environments are
-   propagated.  If the *locals* dictionary is omitted it defaults to the *globals*
-   dictionary.  If both dictionaries are omitted, the expression is executed in the
-   environment where :func:`eval` is called.  The return value is the result of
+   inserted under that key before *expression* is parsed.  This means that
+   *expression* normally has full access to the standard :mod:`builtins`
+   module and restricted environments are propagated.  If the *locals*
+   dictionary is omitted it defaults to the *globals* dictionary.  If both
+   dictionaries are omitted, the expression is executed with the *globals* and
+   *locals* in the environment where :func:`eval` is called.  Note, *eval()*
+   does not have access to the :term:`nested scope`\s (non-locals) in the
+   enclosing environment.
+
+   The return value is the result of
    the evaluated expression. Syntax errors are reported as exceptions.  Example:
 
       >>> x = 1