python求约数的问题

[Linuxwell]

这个函数求数字的最大约数，也会提示这个数是否为素数。
def showMaxFactor(num):
count=num/2
while count>1:
if num%count==0:
print'largest factor of %d is %d'% (num,count)
break
count-=1
else:
print num, "is prime"
#调用这个函数：
for i in range(10,30):
showMaxFactor(i)
#得到结果：
largest factor of 10 is 5
11 is prime
largest factor of 12 is 6
13 is prime
largest factor of 14 is 7
largest factor of 15 is 5
largest factor of 16 is 8
17 is prime
largest factor of 18 is 9
19 is prime
largest factor of 20 is 10
largest factor of 21 is 7
largest factor of 22 is 11
23 is prime
largest factor of 24 is 12
largest factor of 25 is 5
largest factor of 26 is 13
largest factor of 27 is 9
largest factor of 28 is 14
29 is prime
我的问题是代码中的count-=1是什么意思，因为count=num/2,所以我不懂count-=1的作用是什么？

[iambic]

相当于：

count = count - 1

[zhifeng543]

从num/2开始逆向遍历(count没运行一次减1)，找到的第一个大于1的整数就是num的最大约数，否则就是素数。

[iambic]

汗……
就是个循环遍历啊。不去掉的话不就死循环了。

[iambic]

去掉的话不就死循环了。

[Linuxwell]

谢谢大家！！！

[Linuxwell]

我当然知道是count=count-1，我的意思是在代码中起到什么作用。，为什么要这一步。