Python：使用布尔值作为返回值的列表理解

Question

B is a quadratic matrix of size k .

I tried the following code

if [x for x in range(k) if B[x,1] == 1]:

to get:

For the first x in range(k-1) , for which B[x,1] == 1 , stop the for-loop and return true , such that the if-statement can be executed. If there is no such x , then return false and go on in the following code.

Answer 1

看起来你想要any() ：

if any(B[x,1] == 1 for x in range(k)):

Answer 2

arshajii's answer is probably right, but if you also want to have the value of the first x fulfilling your condition you could do:

try:
    x = next(x for x in range(k) if B[x, 1] == 1)
    # Do something with x
except StopIteration:
    # Do something else

---

EDIT: Better yet, thanks @arshajii:

x = next(x for x in range(k) if B[x, 1] == 1, None)
if x is not None:
    # Do something with x
else:
    # Do something else