将两个for循环合并为一个for循环答案

【问题标题】：Merge two for-loops into one for-loop将两个for循环合并为一个for循环
【发布时间】：2018-10-10 13:41:25
【问题描述】：

此代码的目标是确定一个数字是否为素数，如果不是，则打印给定数字可以除以的数字。

我的问题是：是否可以在下面的代码中将两个for 循环合并为一个for 循环？

num = 224

list1 = []

for i in range(2, num):
    if num % i == 0:
        list1.append(i)

for i in range(2, num):
    if num % i == 0:
        print(num, 'is not prime and can be divided by the following numbers:\n', list1)
        break
else:
    print(num, 'is Prime.')

【问题讨论】：

你试过了吗？发生了什么？
@roganjosh 这是第二个循环写入的消息的参数。
@chepner 哎呀，错过了。循环看起来仍然很不稳定。我看不出他们一直想打印整个列表。

标签： python for-loop if-statement primes

【解决方案1】：

由于您已经使用第一个循环中的所有除数构造了 list1，因此您可以在条件中使用它，而不是第二次遍历相同的序列：

for i in range(2, num):
    if num % i == 0:
        list1.append(i)
if list1:
    print(num, 'is not prime and can be divided by the following numbers:\n', list1)
else:
    print(num, 'is Prime.')

【讨论】：

【解决方案2】：

根据给出的答案，重新设计代码的最佳方法是：

num = 224

list1 = [i for i in range(2, num) if num % i == 0]

if list1:
    print(num, 'is not prime and can be divided by the following numbers:\n', list1)
else:
    print(num, 'is Prime.')

谢谢@matthieu-brucher 和@blhsing

【讨论】：

【解决方案3】：

应该这样做，例如 10 个数字：

n = 10

for i in range(2, n + 1):
    divisors = []
    for j in range(2, i):
        if i % j == 0:
            divisors.append(j)
    if divisors:
        print('{} is not prime and can be divided by the following numbers: {}.'.format(i, divisors))
    else:
        print('{} is prime.'.format(i))

输出：

2 is prime.
3 is prime.
4 is not prime and can be divided by the following numbers: [2].
5 is prime.
6 is not prime and can be divided by the following numbers: [2, 3].
7 is prime.
8 is not prime and can be divided by the following numbers: [2, 4].
9 is not prime and can be divided by the following numbers: [3].
10 is not prime and can be divided by the following numbers: [2, 5].

【讨论】：

【解决方案4】：

不需要第二个for循环

num = 224

list1 = []

for i in range(2, num):
    if num % i == 0:
        list1.append(i)

if (not list1):
    print(num, 'is Prime.')
else:
    print(num, 'is not prime and can be divided by the following numbers:\n', list1)

【讨论】：

if (not list1): 中不需要括号。此外，此答案与@blhsing 中的答案几乎相同