python - printing something in a for loop every n seconds

Question

I have a for loop that iterates over a number and performs some simple calculations. I am trying to figure out how to print out ( or log to file) the current value of 'val' every .5 to 1 second with out having to pause or sleep during the loop. Here is a super simple example

val_list = []

for i in xrange(iterations):
    val = (i*(1/2)) * pi
    val2 = np.linalg.pinv(val)
    # print or write to log val2 after every half second (or 1 second)
    val_list.append(val2)

score 4 · Accepted Answer · answered May 07 '15 at 17:11

Just use time.time to capture the time before starting, then check how long it's been after you calculate val2:

import time

val_list = []

prev_time = time.time()

for i in xrange(iterations):
    val = (i*(1/2)) * pi
    val2 = np.linalg.pinv(val)
    # print or write to log val2 after every half second (or 1 second)
    dt = time.time() - prev_time
    if dt > 1:
        # print or write to log here
        prev_time = time.time()    
    val_list.append(val2)

score 1 · Answer 2 · answered May 07 '15 at 17:11

1

You can use time.time():

from time import time as t
val_list = []
nowTime = t()
for i in xrange(iterations):
    val = (i*(1/2)) * pi
    val2 = np.linalg.pinv(val)
    curTime = t()
    if curTime - nowTime >= 0.5:
        #Do your stuff
        nowTime = curTime
    val_list.append(val2)

answered May 07 '15 at 17:11

user1823

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beat me by 5 seconds! – bj0 May 07 '15 at 17:12
You can use time.sleep() also. – user3653796 May 07 '15 at 17:12
@user3653796 the OP said he can't sleep or pause. – user1823 May 07 '15 at 17:13
Same as above, this works for what I need to do. Thank you for the assistance! – user982599 May 07 '15 at 18:34

score 1 · Answer 3 · edited May 23 '17 at 12:14

You can achieve this using Threads.

Here's a documentation on how to utilize Threads : https://docs.python.org/3/library/threading.html ( If you're using Python2.7 then change the 3 in the url to a 2 )

Here's a link which is similar to what you want and should also point you in the right direction : Python threading.timer - repeat function every 'n' seconds

Basically you have to create a Thread that will only execute ever n number of seconds. On each iteration it will print the value. The above link should suffice for that. Good luck !

python - printing something in a for loop every n seconds

3 Answers3