有没有办法在 python 的 if 语句中结合成员比较？

Question

I want to check multiple conditions in an if-statement

if a:
    # do something

a 在这种情况下对多种情况都成立 a==1, a==2, a==3

而不是写

if a == 1 or a == 2 or a == 3:
    # do something

我正在尝试这样的事情

if a == condition for condition in [1, 2, 3]:
    # do something

Answer 1

最简单的写法就是if a in (1, 2, 3)

你想写的可以写成

if any(a == condition for condition in [1, 2, 3])

Answer 2

你走在正确的道路上。需要的是：

if a in [1,2,3]:
   do something

替代

if a == 1 or a == 2 or a ==3:

正如 jonrsharpe 正确指出的那样，也许您正在尝试

if any( a==condition for condition in [1,2,3] ):

这也是一样的。

Answer 3

The truth value of an array with more than one element is ambiguous 看起来像一个 numpy 错误消息。如果 a 是一个 numpy ndarray 并且 b 包含您要测试的值，您可以这样做。

import numpy as np
a = np.arange(6)
b = np.array([6,2,9])
if np.any(a == b[:, None]):
    ...

或

np.any(a[:,None] == b)

利用了broadcasting.

可以使用 my 数组重现您的异常 ...

>>> if a == b[:, None]:
    pass

Traceback (most recent call last):
  File "<pyshell#281>", line 1, in <module>
    if a == b[:, None]:
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
>>>

Answer 4

只是为了补充其他答案，你最好的选择肯定是这个逻辑：

if a in set([1, 2, 3]):
    #do something

甚至更好

 if a in {1, 2, 3}:
    #do something

我想在这里强调的是，在这种情况下您应该使用 set。查找会更有效率。

此外，python documentation 推荐。

Common uses include membership testing, removing duplicates from a sequence, and computing mathematical operations such as intersection, union, difference, and symmetric difference

有没有办法在 python 的 if 语句中结合成员比较？

Is there a way to combine memberwise comparison within an if-statement in python?

python

numpy

if-statement

comparison-operators

multiple-conditions