executing a while loop between defined time

Question

I'm trying to execute a while loop only under a defined time like this, but the while loop continues its execution even when we are above the defined limit :

import datetime
import time

now = datetime.datetime.now()

minute = now.minute

while minute < 46 :
    print "test"
    time.sleep(5)
    minute = now.minute

How can stop the loop once we cross the limit ?

Thanks

Answer 1

You're not updating the value of minute inside while loop properly. You should recalculate the value of now in loop and then assign the new now.minute to minute.

while minute < 46 :
    print "test"
    time.sleep(5)
    now = datetime.datetime.now()
    minute = now.minute

Answer 2

You need to determine the time anew in your loop. The minute variable is static, it does not update to reflect changing time.

If you want to loop for a certain amount of time, start with time.time() instead and then calculate elapsed time:

import time

start = time.time()

while time.time() - start < 300:
    print 'test'
    time.sleep(5)

will print 'test' every 5 seconds for 5 minutes (300 seconds).

You can do the same with datetime objects of course, but the time.time() call is a little simpler to work with.

To loop until a certain time datetime can be used like:

import datetime

while datetime.datetime.now().minute < 46:
    print 'test'
    time.sleep(5)

Again, note that the loop needs to call a method each time to determine what the current time is.

Answer 3

The loop's proposition should be datetime.datetime.now().minute - minute < 46 and the body of the loop shouldn't be updating minute.