Python中nonlocal關鍵字

在這篇文章中介紹了“Python的閉包與nonlocal”的用法，因為nonlocal是在Python3.0中新增的關鍵字，python2.x不提供支援，文中提出在Python2.x解決巢狀函式引用外部變數的方法只有使用global 關鍵字定義全域性變數，另一種可行的解決方案是使用列表或字典代替要操作的關鍵字。

示例如下：

1.python3.0 使用nonlocal關鍵字

>>> def outer():
        x = 1
        def inner():
            nonlocal x
            x = 2
            print("inner:", x)
        inner()
        print("outer:", x)
 
 >>> outer()
 inner: 2
 outer: 2

2.python2.x  藉助list或dict實現

>>> def outer():
        x = [1]
        def inner():
            x[0] += 1 #修改x[0]儲存的值
            print("inner:", x[0])
        inner()
        print("outer:", x[0])
 >>> outer()
 inner: 2
 outer: 2

更多參考資料：

1. http://stackoverflow.com/questions/1261875/python-nonlocal-statement

2.javascript中作用域鏈定義與python作用域的異同

3.官方文件：

“The nonlocal statement causes the listed identifiers to refer to previously bound variables in the nearest enclosing scope. This is important because the default behavior for binding is to search the local namespace first. The statement allows encapsulated code to rebind variables outside of the local scope besides the global (module) scope.

Names listed in a nonlocal statement, unlike to those listed in a global statement, must refer to pre-existing bindings in an enclosing scope (the scope in which a new binding should be created cannot be determined unambiguously).

Names listed in a nonlocal statement must not collide with pre-existing bindings in the local scope.“