求助，编写素数函数程序题目，谢谢各位

import math
def isPrime(q):
    if q <= 1:
        return False
    tmp = int(math.sqrt(q))
    for i in range(2, tmp+1):
        if q % i == 0:
            return False
    return True
def decompose(os):
    flag = False
    if os % 2 != 0 or os < 2:
        print("数字必须为大于2的偶数")
    else:
        for i in range(2,int(os/2)+1):
            if isPrime(i) and isPrime(os-i):
                print("{}+{}={}".format(i,os-i,os))
                flag = True
                break
        if not flag:
            print("找不到")