In symtable.Function.get_locals() symbols with scopes in (LOCAL, CELL) are selected. Also

>>> code = """\
... def foo():
...    x = 42
...    def bar():
...       return x
... """
>>> import symtable
>>> top = symtable.symtable(code, "?", "exec")
>>> top.get_children()[0].lookup('x')._Symbol__scope == symtable.CELL
True

So I guess this would be the correct fix then:

def is_local(self):
    return self.__scope in (LOCAL, CELL)