python中nonlocal关键字是什么

x = 1

def func():

    nonlocal x

    x =2

    print(x)

func()

print(x)

结果代码报错，SyntaxError: no binding for nonlocal 'x' found

x = 1

def func():

    x = 2

    def subfunc():

        nonlocal x

        x = x + 1

        print('subfunc内打印的值：%d' % x)

        return x

    print('func内打印的值：%d' % x)

    return subfunc

func()

print('func外打印的值：%d' % x)

结果是：

func内打印的值：2

func外打印的值：1