Question

Hello guys. Starting on problem set 1, problem 1. I figured it would help me to write a function for prime numbers before I moved on to the next part of the problem. However, thats not working very well. http://dpaste.com/547820/ The issue is that a prime number, say 5, would meet the conditions i ask in the script and it would print at the end, but so would the number 4, which is not a prime number.

Answer 1

Hoot! You just asked your first question! Hang tight while I find people to answer it for you. You can thank people who give you good answers by clicking the 'Good Answer' button on the right!

Answer 2

All numbers will fit the first condition, divide anything by 1 and you are left with the same number. Divide anything by itself and there will be no remainder.

Therefore, it will print x if y can't be divided into it, or it will do nothing otherwise.

Your example prints 4 because you can't divide 3 into 4 (evenly), even though you can divide 2 into 4 (you are not checking for that).

Answer 3

I don't know if it helps, but I just finished this assignment, and the first thing I did in my function was check to see if any test number divided by either 2 or 3 had a remainder. That eliminates any even numbers and multiples of 3.

Answer 4

Here is what I came up with and it appears to work:


def isPrime(cand):

prime = None

if (cand==1) or (cand%2==0 and cand!=2):
prime = False

else :
for divisor in range(3,(cand/3+1),2):
if cand%divisor==0:
prime = False

if prime == False:
return False
else:
return True

Calling isPrime(cand) will return either True or False
eg.
>>> isPrime(9)
False
>>> isPrime(7919)
True

Hope this helps :)