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())
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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())
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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
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