遍历数字并评估数字是否可被某些数字整除 [英] loop through numbers and evaluate if numbers are divisible by certain numbers

问题描述

我写了一个程序来评估某个范围内的哪些数字只能被某些数字(在 1 到 9 范围内)整除.到目前为止，该代码似乎仍然有效，但是我在pythontutor http://www.pythontutor.com/visualize.html#mode=edit ，发生了一些奇怪的事情.

i wrote a program to evaluate what numbers in a certain range are divisble by only certain numbers (in the range 1 to 9). So far the code seems to work but i tested the steps it takes through at pythontutor http://www.pythontutor.com/visualize.html#mode=edit and something odd happened.

在第二个循环中，代码并不总是检查所有值(k)的可除性，但有时会忽略最后一个值(k).最好给你一个例子:

In the second loop, the code doesnt always check all values (k) for its divisibility but sometimes leaves out the last value (k). Better to give you an example:

Liste = []
for i in range (1500, 1700):
    if i%5 == 0 and i%7 == 0:
        Liste.append(i)
print (Liste)

Teiler = [2, 3, 4, 6, 8, 9]
for k in Liste:
    z = 0
    for w in range (len(Teiler)):
        if k%Teiler[z] == 0:
            Liste.remove(k)
            z += 1
            break
        else:
            z += 1

print (Liste)

这里的输出如下:

[1505, 1540, 1575, 1610, 1645, 1680]

[1505, 1575, 1645]

其输出(如第二个列表所示)应该是被 5 和 7 整除的数字.同样在pythontutor上，第二个for循环遍历所有值(k).

And its the output that its supposed to be, as in the second list are only the numbers divisible by 5 and 7. Also on pythontutor the second for loop goes through all values (k).

但是当我像下面那样更改数字范围时(第2行，将范围从 1700 更改为 1800 ):

But when i change the range of number like the following (line 2, change range from 1700 to 1800):

Liste = []
for i in range (1500, 1800):
    if i%5 == 0 and i%7 == 0:
        Liste.append(i)
print (Liste)

Teiler = [2, 3, 4, 6, 8, 9]
for k in Liste:
    z = 0
    for w in range (len(Teiler)):
        if k%Teiler[z] == 0:
            Liste.remove(k)
            z += 1
            break
        else:
            z += 1

print (Liste)

输出如下:

[1505, 1540, 1575, 1610, 1645, 1680, 1715, 1750, 1785]

[1505, 1575, 1645, 1715, 1785]

如果我在pythontutor上运行此代码，则代码在 k = 1750 处停止，并且不检查 k = 1785 .

If i run this code on pythontutor, the code stops at k = 1750 and doesnt check for k = 1785.

为什么会这样?检查pythontutor是否有问题?还是我的代码有问题?

Why is it behaving that way? Is it a problem with the check on pythontutor? Or is there a problem with my code?

我想了解Python为什么要这样做.

I want to understand why Python is doing what it does.

非常感谢您的帮助.我很抱歉，如果这是一个菜鸟问题，或者我错过了明显的东西.

Thank you very much for your help. Iam sorry if this is a noob question or iam missing out something obvious.

推荐答案

请勿从您迭代过的列表中删除项目，因为其他答案都已说明.更改列表的长度会影响迭代.示例:

Don't remove items from the list you iterate over, as the other answer states. Changing the length of the list affects the iteration. Example:

>>> L=list(range(10))
>>> for i in L:
...   if i==5: L.remove(i)
...   print(i)
...
0
1
2
3
4
5  # removed 5, and skipped 6!
7
8
9

也不会使用 w ，尽管 z 是等效的.而是直接在 Teiler 上进行迭代，并在满足条件的情况下将项目添加到新列表中:

Also w is never used, although z is the equivalent. Instead, iterate directly over Teiler and add items to a new list if it satisfies your condition:

Liste = []
for i in range (1500, 1800):
    if i%5 == 0 and i%7 == 0:
        Liste.append(i)
print (Liste)

Liste2 = []
Teiler = [2, 3, 4, 6, 8, 9]
for k in Liste:
    for w in Teiler:
        if k % w == 0:
            break
    else:
        Liste2.append(k)

print(Liste2)

输出:

[1505, 1645, 1715]

如果您没有看到 for/else ，则只有在不中断 for 循环的情况下才会执行 else ，因此 k％w！= 0 的所有值都必须为true.

If you haven't seen for/else, the else only executes if you don't break from the for loop, so all of k % w != 0 has to be true.

另一种选择是使用列表理解，真正简化了代码:

Another option is to use list comprehensions, which really simplify the code:

L = [i for i in range(1500,1800) if i%5 == 0 and i%7 == 0]
L = [x for x in L if all(x % k != 0 for k in (2,3,4,6,8,9))]
print(L)

输出:

[1505, 1645, 1715]

注释1575和1785可被3整除，因此您的两个样本列表都因删除列表中的值而出错.

Note 1575 and 1785 are divisible by 3, so both your sample lists had errors from removing values in the list.

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