co_freevars question

[Jeff Epler]

co_freevars names variables that come from an enclosing scope that is
not module scope.

def g():
    return y
print g.func_code.co_freevars       # ()

def f():
    y = 3
    def g(): 
        return y
    print g.func_code.co_freevars   # ('y',)
f()

Jeff