python中global与nonlocal比较

python引用变量的顺序： 当前作用域局部变量->外层作用域变量->当前模块中的全局变量->python内置变量

一、global

global关键字用来在函数或其他局部作用域中使用全局变量。但是如果不修改全局变量也可以不使用global关键字。

gcount = 0

def global_test():

    print (gcount)

    

def global_counter():

    global gcount

    gcount +=1

    return gcount

    

def global_counter_test():

    print(global_counter())

    print(global_counter())

    print(global_counter())

二、nonlocal

nonlocal关键字用来在函数或其他作用域中使用外层(非全局)变量。

def make_counter():

    count = 0

    def counter():

        nonlocal count

        count += 1

        return count

    return counter

    

def make_counter_test():

  mc = make_counter()

  print(mc())

  print(mc())

  print(mc())

也可以使用generator来实现类似的counter。如下：

def counter_generator():

    count = 0

    while True:

        count += 1

        yield count

    

def counter_generator_test():

  # below is for python 3.x and works well

  citer = counter_generator().__iter__()

  i = 0

  while(i < 3) : 

    print(citer.__next__())

    i+=1

  

def counter_generator_test2():  

  #below code don't work

  #because next() function still suspends and cannot exit

  #it seems the iterator is generated every time.

  j = 0

  for iter in counter_generator():

    while(j < 3) : 

      print(iter)

      j+=1