更改代码块内 for 循环的迭代器

Question

Suppose I have a code block like,

for i in range(15):
    print(i)
    i+=5

I expect the i value at each iteration should be i = 0,5,10, ....

Even though I am changing the iterator inside the code block of for loop, the value is not affecting the loop.

Can anyone explain the functionality happening inside?

Answer 1

Here, you're defining i as a number from 0 to 14 everytime it runs the new loop. I think that what you want is this:

i = 0
for _ in range(15):
    print(i)
    i += 5

Answer 2

A for loop is like an assignment statement. i gets a new value assigned at the top of each iteration, no matter what you might do to i in the body of the loop.

The for loop is equivalent to

r = iter(range(15))
while True:
    try:
        i = next(r)
    except StopIteration:
        break
    print(i)
    i += 5

Adding 5 to i doesn't have any lasting effect, because i = next(r) will always be executed next.

Answer 3

As the others have said, range emits the number and your assignment doesn't matter.

To get the desired result use something like

for i in range(0, 15, 5):
    print(i)