Question

I work on a windows XP PC with a Python 2.6 install and I was trying to solve a Project Euler problem, but whenever I execute the code the interpreter hangs. I’ve debugged it through PyScripter, IDLE and MonkeyStudio, but it still doesn’t work even for trivial values like 15.

I simply don’t understand why. Can you please help me out?

Here’s the code:

"""Project Euler Problem 3
Author: A"""

num = 15
prime = [1]
x = long (round(num/2))

def ifprime (x): 
        """ Defining the function that checks if the number is prime or not"""    
        """ Checking if the passed number is prime or not"""

        y = long(round(x/2))
        while y > 0:
                if x%y == 0:
                        return False
                y -= 1
        return True

while x > 0:
    if num%x == 0:
        if ifprime(x):
                print "I've found a prime! "
                print x
                prime[len(prime):] = [x]
        x -= 1

Answer 1

Your x -= 1 statement is indented one level too far.

x will only be decremented when num % x is 0

It should be this:

while x > 0:
    if num%x == 0:
        if ifprime(x):
                print "I've found a prime! "
                print x
                prime[len(prime):] = [x]
    x -= 1