我正在尝试在循环中使用break语句。我正在尝试构建一个函数，该函数查找小于用户给定数字的最大质数userInput。这是我的代码：
def primeFinder():
aVar = 2 # This is a possible factor
divisorList = [] # This is a factor list of userInout, the inputted number
while aVar <= userInput: # Checking until the variable cannot be a factor
if userInput % aVar == 0: # If userInput divided by the variable has a remainder of zero, it means it is a factor
divisorList.append(aVar) # Adding the factor to th factor list
aVar+=1 # Making the possible factor numeral one bigger to test again
else:
aVar +=1 # Making the possible factor numeral one bigger to test again
print divisorList
if len(divisorList) > 1: # If there are more than one factor...
print "Your input",userInput, " is not prime" # It is not prime
else:
print "Your input", userInput," is prime." # It is prime
当我找到最大的素数时，我需要知道在哪里放置break语句来停止程序。我放在哪里，为什么放？返回功能不起作用。这是发生了什么：
[2, 4, 5, 8, 10, 20, 25, 40, 50, 100, 125, 200, 250, 500, 1000]
Your input 1000 is not prime
[3, 9, 27, 37, 111, 333, 999]
Your input 999 is not prime
[2, 499, 998]
Your input 998 is not prime
[997]
Your input 997 is prime.
[2, 3, 4, 6, 12, 83, 166, 249, 332, 498, 996]
Your input 996 is not prime
[5, 199, 995]
Your input 995 is not prime
[2, 7, 14, 71, 142, 497, 994]
Your input 994 is not prime
[3, 331, 993]
Your input 993 is not prime
[2, 4, 8, 16, 31, 32, 62, 124, 248, 496, 992]
Your input 992 is not prime
[991]
Your input 991 is prime.
[2, 3, 5, 6, 9, 10, 11, 15, 18, 22, 30, 33, 45, 55, 66, 90, 99, 110, 165, 198, 330, 495, 990]
Your input 990 is not prime
当n太大时，请尝试使用xrange以获得更好的性能：
from math import sqrt
def is_prime(n):
if n in (2, 3):
return True
for i in xrange(2, int(sqrt(n)) + 1):
if n % i == 0:
return False
return True
def find_largest_prime(n):
for i in xrange(n - 1, 1, -1):
if is_prime(i):
return i
print(find_largest_prime(1000))
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