如何使我的for循环只打印一次，而不是为i的每个值打印

Question

我正在尝试创建一个函数来检查作为参数的给定数字是否为质数。我决定用一个for循环来做这件事，但它一直打印出这个数对于某些除数来说不是质数，而对于其他数来说它是质数。下面是我的代码：

def prime(n):
    for i in range(2, n):
        if n%i == 0:
            print (n," is not prime because it is divisible by ", i)

        else:
            print (n, " is a prime number")


prime (15)

这是输出：

15  is a prime number
15  is not prime because it is divisible by  3
15  is a prime number
15  is not prime because it is divisible by  5
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number
15  is a prime number

因此，我不想把这个作为输出，而是立即认识到，如果这个数有除数1和它本身以外的除数，它就不是质数。如果数字不是这样的话。就像这样：

#if number if prime
15 is a prime number

#if number is not prime
15 is not a prime number because it is divisible by 3

Answer 1

通过returning，一旦识别出一个数字不是质数，该函数就会停止。

def prime(n):
    for i in range(2, n):
        if n%i == 0:
            print (n," is not prime because it is divisible by ", i)
            return 
    print (n, " is a prime number")
    return

这样做的好处是，一旦表达式n%i == 0的计算结果为真，它就会打印并返回，从而停止进一步的不必要的计算。

Answer 2

尝尝这个

def prime(n):
    for i in range(2, n):
        if n%i == 0:
            print (n," is not prime because it is divisible by ", i)

prime (15)

Answer 3

我会尝试这样的方法：

def prime(n): 
    isprime = True
    for i in range(2, n): 
         if n%i == 0:
              print (n," is not prime because it is divisible by ", i)
              isprime = False
              break
    if isprime:
         print (n, " is a prime number")
prime (15)