python - 列表理解python中的复杂if表达式

Question

我在列表理解中有这个 if 表达式：

[(i,j,k) for i in S for j in S for k in S 
 if ((i+j+k==0) and (i!=0) and (j!=0) and (k!=0))]

但它似乎不是在我的条件之间进行评估，而是在或之间进行评估。为什么会这样？

问题是当 i,j 和 k 之一为 0 时，不添加元组，这不是我想要的。我只想在它们都为 0 时发出。即：我希望结果中包含 0,3,-3。

Answer 1

If you still want a one-liner, then the following is actually readable:

[i for i in itertools.product(range(-3, 3), repeat=3) 
 if any(i) and sum(i) == 0]

Answer 2

(i,j,k)要仅在它们都为零时省略，请使用条件(i,j,k) != (0,0,0)：

S = range(-3,3)
x = [(i,j,k)
     for i in S
     for j in S
     for k in S
     if ((i+j+k==0)
         and (i,j,k) != (0,0,0))]
print(x)

印刷

[(-3, 1, 2), (-3, 2, 1), (-2, 0, 2), (-2, 1, 1), (-2, 2, 0), (-1, -1, 2), (-1, 0, 1), (-1, 1, 0), (-1, 2, -1), (0, -2, 2), (0, -1, 1), (0, 1, -1), (0, 2, -2), (1, -3, 2), (1, -2, 1), (1, -1, 0), (1, 0, -1), (1, 1, -2), (1, 2, -3), (2, -3, 1), (2, -2, 0), (2, -1, -1), (2, 0,
-2), (2, 1, -3)]

---

要了解原始条件出了什么问题，请(i!=0) and (j!=0) and (k!=0)：

考虑当i=0和时会发生什么j=1：

| i != 0 | j != 0 | (i!=0) and (j!=0) | (i,j) != (0,0) |
| False  | True   | False             | True           |

(i!=0) and (j!=0)是False因为False and True是False。相反，(i,j) != (0,0)总是True，除非两者i都j为零。

添加(k!=0)使示例更复杂，但想法是相同的。

Answer 3

You could simplify this greatly using itertools...

from itertools import combinations_with_replacement as icwr

S = [t for t in icwr(range(-3,3),3) if t != (0,0,0)]

print S

This is much simpler... (if it is what you want to do!)