Generator function not updating a local variable

Question

I'm working on a problem that I got from a friend, in this problem I need to generate the time in the following format: 00:00:00, 00:00:01, 00:00:02 etc... But to follow the instructions of this problem correctly I need to use generator functions to accomplish that result. So first of all I need to create three generator functions that generate numbers between 0-59 for secs and mins and 0-23 for hrs. so I tried to do it, and I think that I did everything correctly but I encountered a problem, let's say that we're talking about the gen_func that generates hours for now (I will call it gen_hr), when I try to use the yield command it works, but it only prints to the screen the number 0 which should be only the beggining of what I really want, I'm trying to update the local variable (it's local to the gen_hr generator function), but it's not updating, everytime I try to print the next produced value it prints 0. HERE'S THE CODE:

def gen_hours():
    hr = 0

    while hr < 24:
        if hr < 10:
            yield f"0{hr}"
            hr += 1
        else:
            yield hr
            hr += 1

AND HERE'S THE OUTPUT:

for i in range(10):
    print(next(gen_hours()))

>>> 00
>>> 00
>>> 00
>>> 00
>>> 00
>>> 00
>>> 00
>>> 00
>>> 00
>>> 00

HERE IS THE OUTPUT THAT I WAS EXPECTING:

>>> 01
>>> 02
>>> 03
>>> 04
>>> 05
>>> 06
>>> 07
>>> 08
>>> 09
>>> 10

It would be wonderful if you help me understand what's wrong with my code.

Answer 1

you should first create a generator and then call next on it:

gen = gen_hours()
for i in range(10):
    print(next(gen))

a different way to achieve just that using islice is:

from itertools import islice

for h in islice(gen_hours(), 10):
    print(h)

you code creates a fresh generator in each iteration of the loop and calls next to always get the first element.