为什么sum=0.0放在开头会报错？

sum = 0.0
def average(*args):
    if len(args) == 0:
            return sum
    for x in args:
            sum = sum + x
    return sum/len(args)
print average()
print average(1, 2)
print average(1, 2, 2, 3, 4)

Traceback (most recent call last):
File "index.py", line 8, in
print average()
File "index.py", line 4, in average
return sum
UnboundLocalError: local variable 'sum' referenced before assignment

标答的sum=0.0放在def之后，为什么放在开头就会报错？

qq_慕雪8441108

2019-07-20

源自：初识Python 7-7

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2 回答

慕婉清2588457
2019-07-20

如果需要全局变量

global sum sum = 0.0
def average(*args):    
    global sum
    sum = 0.0
    if len(args) == 0:
        return sum
    for x in args: 
        sum = sum + x
        return sum/len(args)
    print average()
    print average(1, 2)
    print average(1, 2, 2, 3, 4)