如何引用不同作用域和名称空间，以及 ​​global​​​ 和 ​​nonlocal​​ 对变量绑定的影响：

def scope_test():
    def do_local():
        spam = "local spam"

    def do_nonlocal():
        nonlocal spam
        spam = "nonlocal spam"

    def do_global():
        global spam
        spam = "global spam"

    spam = "test spam"
    do_local()
    print("After local assignment:", spam)
    do_nonlocal()
    print("After nonlocal assignment:", spam)
    do_global()
    print("After global assignment:", spam)

scope_test()
print("In global scope:", spam)

示例代码的输出是：

After local assignment: test spam
After nonlocal assignment: nonlocal spam
After global assignment: nonlocal spam
In global scope: global spam

注意，局部 赋值（这是默认状态）不会改变 scope_test 对 spam 的绑定。 nonlocal 赋值会改变 scope_test 对 spam 的绑定，而 global 赋值会改变模块层级的绑定。

而且，global 赋值前没有 spam 的绑定。