Question

# this program will test numbers and check if they are prime numbers or even numbers

num = eval(input('Enter a number: '))#generating user input
for i in range(num):
    x = 2
    if num % 2 == 0: #test for even numbers
        print(num, x, 'is even')
    else:
        while num % x != 0:#the idea here is to enter a loop and test the numbers against x=2, x +=1... to check if they are divisible
            x += 1         #by x
            break
        if num % x == 0:    #x is however either 2 or 3. it never advances to four and numbers like 25 become prime numbers
            print(num,x, 'is odd')
        else:
            print(num,x, 'is prime')
    num -=1

代码中存在逻辑缺陷我无法弄清楚它在哪里

Answer 1

改变这个：

num = eval(input('Enter a number: '))

要：

num = input('Enter a number: ')
if num.is_digit(): #evaluate if is a number
    num = int(num)
else:
    #broke code logic
    num = 0

Answer 2

您可以使用以下方法更快地测试素数：

List

在您的代码中：

num > 1 and all(num % i for i in xrange(2, sqrt(num)))

Answer 3

你的基本问题在于这个块：

while num % x != 0:
    x += 1
    break

...你有一个无条件break，这意味着循环永远不会运行多次。比较

def is_prime(n):
    if n < 4:
        return n in {2, 3}
    elif not n % 2:
        # even
        return False
    else:
        return all(n % div for div in range(3, int(n ** 0.5 + 1.), 2))

然后您的程序看起来像

def main():
    print("Show all primes up to what number?")
    upto = int(input(": "))
    for n in range(2, upto + 1):
        if is_prime(n):
            print("{} is prime".format(n))
        else:
            print("{} is {}".format(n, ["even", "odd"][n % 2]))
main()

素数查找器，它在python中

3 个答案: