python - Why does this script get stuck in infinite loop for some cases? -


i'm re-working old python script. while running through random test cases, i'm noticing stuck in infinite loop cases, not others. script project euler problem 3 (works question prompt, never noticed random infinite loops). work 10, 19, 51, 600851475143. gets stuck in infinite loop 152. haven't tried others, thought enough test cases notice 'odd'.

here's code:

import sys  def largestprime(n):     largest_prime = 0 # initialize largest prime     d = 2 # set first value factor evaluation      while n > 1: # n divided each factor later on         while n % d == 0: # check if n divisible factor             if d > largest_prime: # check if d greater largest_prime                 largest_prime = d # if so, set largest_prime = d                 n /= d # if so, can divide n d find remaining factors         d += 1      return largest_prime   def main():     # make list of command line arguments, omitting [0] element     # script itself.     args = sys.argv[1:]     if not args: #if list empty; return message & exit         print ("usage: euler003.py 'n'")         sys.exit(1)      if len(args) > 1: #if list less 1; return message & exit         print ("you've entered many arguments; usage: euler001.py 'n'")         sys.exit(1)      largest = largestprime(int(args[0]))     print (largest)   # standard boilerplate calls main() function.     if __name__ == "__main__":     main()

placen/=d outside if (but inside while) in def largestprime(n): because in code, n/=d when d greater largest_prime wrong. n/=d must done till n % d == 0

while n % d == 0:      if d > largest_prime:        largest_prime = d      n /= d  d += 1

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