python数组求和与平均值

ls=[4,9,19,8,391,39,9,283,45]
sum(ls)
average=sum(ls)/len(ls)
print('累加值',sum(ls),'平均值',average)

#求数组元素的平均值
 
a=[1,4,8,10,12]
b=len(a)
sum=0
print "数组长度为：",b
for i in a:
    sum=sum+i
print "均值为：",sum/b