for循环声明中的函数是否会在Python中多次调用？

Question

There is a function and a for loop:

def helper():
    return [1,2,3]

for i in helper():
    print(i)

I am wondering if the helper function would only be called once at the initialization of the for loop. As I am thinking that if I call the function and assign the return array to a variable in advance, which would be used in the for loop like this:

def helper():
    return [1,2,3]
temp = helper()
for i in temp:
    print(i)

Is that with less time complexity?

Thanks!

Answer 1

use the yield operation:

def helper():
    for i in [1,2,3]:
         yield i

for i in helper():
    print(i)

in this case the helper() method would return the i value during each iteration to the calling for loop.