Question

由于某种原因，当候选人数达到21时，它意识到21可以被3整除，但是后来不会突破for循环/相比之下，例如对于25，则说明25可以被5整除爆发了。

具体来说，当div == 3时，它不会突破循环。这是为什么？

for cand in range (3,100):
    if cand%2 != 0:
        if ((cand ==3) or (cand ==5) or (cand ==7) or (cand ==11) or (cand == 13)):
            print str(cand) + ' is prime.'
        else:
            x = sqrt(cand)
            y= int (x)
            for div in range(3, (y+2)):
                if (cand%div == 0):
                    print div
                    print str(cand) + ' is divisible by' + str(div)
                    div = 10*y
                elif (div == y):
                    print str(cand) + ' is prime.'

以下是代码的输出：

3 is prime.
5 is prime.
7 is prime.
3
9 is divisible by3
11 is prime.
13 is prime.
3
15 is divisible by3
17 is prime.
19 is prime.
3
21 is divisible by3
21 is prime.
23 is prime.
5
25 is divisible by5
3
27 is divisible by3
27 is prime.
29 is prime.
31 is prime.
3
33 is divisible by3
33 is prime.
5
35 is divisible by5
37 is prime.
3
39 is divisible by3
39 is prime.
41 is prime.
43 is prime.
3
45 is divisible by3
5
45 is divisible by5
45 is prime.
47 is prime.
7
49 is divisible by7
3
51 is divisible by3
51 is prime.
53 is prime.
5
55 is divisible by5
55 is prime.
3
57 is divisible by3
57 is prime.
59 is prime.
61 is prime.
3
63 is divisible by3
7
63 is divisible by7
5
65 is divisible by5
65 is prime.
67 is prime.
3
69 is divisible by3
69 is prime.
71 is prime.
73 is prime.
3
75 is divisible by3
5
75 is divisible by5
75 is prime.
7
77 is divisible by7
77 is prime.
79 is prime.
3
81 is divisible by3
9
81 is divisible by9
83 is prime.
5
85 is divisible by5
85 is prime.
3
87 is divisible by3
87 is prime.
89 is prime.
7
91 is divisible by7
91 is prime.
3
93 is divisible by3
93 is prime.
5
95 is divisible by5
95 is prime.
97 is prime.
3
99 is divisible by3
9
99 is divisible by9

Answer 1

for循环不是while循环。

在Python中，唯一类型的for循环是其他语言中的'foreach' - 它遍历元素列表。在您的情况下，您将遍历范围，即从3到y + 2的整数列表。它是列表中确定迭代何时停止的元素数，而不是其中任何一个的值。当您在循环的一次迭代中更改div时，这对其余项目没有影响。

如果满足条件，您可以使用break突破循环。或者，如果您想保留逻辑，可以尝试使用while，但是您需要手动递增计数器。

Answer 2

您的代码中没有break语句。

Answer 3

Python循环不起作用：

#!/usr/bin/env python
for a in range(1,20):
        print a
        a = 39

考虑：

for a in [32,14,"a",False]:
        print a
        a = True

例如。

Answer 4

相比之下，例如对于25，则音符25可被5整除爆发了。

不，它没有。它还运行div = 6的循环，但没有打印任何内容，因为if条件都没有。您的for循环会在每次迭代开始时设置索引，因此您的div=10*y行完全没有意义。

没有打破for循环

4 个答案: