primes in python

[Loyisile]

I need to implement an algorithm that determines whether a number is prime or not.

[bvdet]

Now that I understand your need, what is your question? Given a number, let's say 21, how would you determine if that number is prime or not on scratch paper?

[RedSon]

Are you trying to determine primes for numbers less than 341,550,071,728 ,321? Or are you planning on using this test in a cryptographic setting?

One is easy... the other will make your brain hurt.

[RedSon]

Here is the brain hurting part: http://www.math.dartmouth.edu/~carlp/

[bazookajoe1]

import math

def isPrime(x):
    """Returns True if x is prime or False if x is not prime."""
    if x <= 1:
        return False
    else:
        y = int(math.sqrt(x))
        while x % y != 0:
            y -= 1
        if y == 1:
            return True
        else:
            return False

[Glenton]

sympy has an isprime function