There are several cases where Python statements are illegal when
used in conjunction with nested scopes that contain free
variables.
If a variable is referenced in an enclosing scope, it is illegal
to delete the name. An error will be reported at compile time.
If the wild card form of import -- "import *" -- is used in a
function and the function contains or is a nested block with free
variables, the compiler will raise a SyntaxError.
If exec is used in a function and the function contains or
is a nested block with free variables, the compiler will raise a
SyntaxError unless the exec explicitly specifies the local
namespace for the exec. (In other words, "exec obj"would be illegal, but "exec obj in ns" would be legal.)
The eval(), execfile(), and input()
functions and the exec statement do not have access to the
full environment for resolving names. Names may be resolved in the
local and global namespaces of the caller. Free variables are not
resolved in the nearest enclosing namespace, but in the global
namespace.4.1The exec statement and the eval() and
execfile() functions have optional arguments to override
the global and local namespace. If only one namespace is specified,
it is used for both.
