factors of a number with memoization code example

Example: factors of a number with memoization

import math

def memoize(f):
    memo = {}
    def helper(x):
        if x not in memo:
            memo[x] = f(x)
        return memo[x]
    return helper

@memoize
def isprime (n):
    if n == 1:
        return False
    elif n == 2:
        return True
    else:
        for x in range (2, int(math.sqrt(n))+1):
            if n % x == 0:
                return False
                break
        else:
            return True


def factors (a):
    if a == 1:
        return []
    elif isprime(a):
        return [a]
    else:
        for x in range (2, int(math.sqrt(a))+1):
            if a % x == 0:
                return [x] + factors(a/x)

testnumber = int(input("Enter a number."))
print factors(testnumber)