[Py006] global vs nonlocal

可参考https://www.cnblogs.com/brad1994/p/6533267.html

global 只能作用于全局环境，针对的是最外层的 x=0

外层函数outer 下的x=1 无法被 global 覆盖，所以最后print("outer:",x) 返回的是1

In[2]: x = 0 
In[3]: def outer():
  ...:     x = 1
  ...:     def inner():
  ...:         global x
  ...:         x = 2
  ...:         print("inner:",x)
  ...:     inner()
  ...:     print("outer:",x)
  ...:     
In[4]: outer()
inner: 2
outer: 1
In[5]: print("global:",x)
global: 2

nonlocal 只能在闭包里面使用

当使用 nonlocal 时候，就声明了x 不知在嵌套函数inner 里有效，而是在整个大函数outer里面都有效

In[6]: def outer():
  ...:     x = 1
  ...:     def inner():
  ...:         nonlocal x
  ...:         x = 2
  ...:         print("inner:",x)
  ...:     inner()
  ...:     print("outer:",x)
  ...:     
In[7]: x=0
In[8]: outer()
inner: 2
outer: 2
In[9]: print("global:",x)
global: 0