Python中关键字nonlocal和global的声明与解析介绍

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a = 10 
 
def foo(): 
 a = 100 

>>> a 
10 
>>> def foo(): 
...  global a 
...  a = 100 
... 
>>> a 
10 
>>> foo() 
>>> a 
100 

def countdown(start): 
 n = start 
 def decrement(): 
  n -= 1 

def countdown(start): 
 n = start 
 def decrement(): 
  nonlocal n 
  n -= 1 

x = 0
def outer():
 x = 1
 def inner():
  x = 2
  print("inner:", x)

 inner()
 print("outer:", x)

outer()
print("global:", x) 

# inner: 2
# outer: 1
# global: 0 

x = 0
def outer():
 x = 1
 def inner():
  nonlocal x
  x = 2
  print("inner:", x)

 inner()
 print("outer:", x)

outer()
print("global:", x) 

# inner: 2
# outer: 2
# global: 0 

x = 0
def outer():
 x = 1
 def inner():
  global x
  x = 2
  print("inner:", x)

 inner()
 print("outer:", x)

outer()
print("global:", x) 

# inner: 2
# outer: 1
# global: 2 

global 是对整个环境下的变量起作用，而不是对函数类的变量起作用。

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