Python 3: Nested while loops based time

Question

I am trying to run two while loops based on an input condition. In this example, that is taken out and replaced by a 1 == 0 so that 0 can be changed back and forth for testing. Once selected, each while loop should run for 10 seconds and then the input condition checked (replaced by 1 == 0) again.

The problem appears to be in the time comparison, since it never evaluates correctly. What am I missing?

#!/usr/bin/env python3
import time 
import os
import bellmod
while True:
    starttime = time.time()
    print("Start time   " + str(starttime)) #Time check
    elapsedtime = 0 #Reset elasped time to 0 for each loop iteration.
    if 1 == 0: #Change this to run either loop. See if remote or local has precidence. 
        while(elapsedtime < 10):
            print("Inside remote while  " + time.strftime("%H:%M:%S")) #Time check
        elapsedtime = time.time() - starttime #Calculate elasped time.
    else:
        elapsedtime = 0
        while(elapsedtime < 10):
            print("inside bottom of local while  " + str(int(time.time() - starttime))) #Time check
        elapsedtime = time.time() - starttime #Calculate elasped time.

Isn't it easier to just use time.sleep(10) to wait ten seconds? — hoefling
– hoefling, Commented Nov 22, 2017 at 17:01
Look closely at your indentation. When do you think elapsedtime is updated? — Martijn Pieters
– Martijn Pieters, Commented Nov 22, 2017 at 17:03
@MartijnPieters: oh, I see - sleeping would mean no prints while sleeping... — hoefling
– hoefling, Commented Nov 22, 2017 at 17:04
When you get to a resolution, please remember to up-vote useful things and accept your favourite answer (even if you have to write it yourself), so Stack Overflow can properly archive the question. — Prune
– Prune, Commented Nov 27, 2017 at 16:18

Martijn Pieters · Accepted Answer · 2017-11-22 17:06:33Z

Your inner while loops are endless, because elapsedtime is never updated:

while(elapsedtime < 10):
    print("inside bottom of local while  " + str(int(time.time() - starttime))) #Time check
elapsedtime = time.time() - starttime #Calculate elasped time.

elapsedtime is updated after the while loop ends, but that is never reached.

You need to fix your indentation so elapsedtime is calculated each loop iteration:

while(elapsedtime < 10):
    print("inside bottom of local while  " + str(int(time.time() - starttime))) #Time check
    elapsedtime = time.time() - starttime #Calculate elasped time.

Note that while is not a function. Using (...) groups the test expression, but is not needed or normally used. If you pass in values as separate arguments to print(), that takes care of including a separator and conversion to string for you:

while elapsedtime < 10:
    print("inside bottom of local while", int(time.time() - starttime))
    elapsedtime = time.time() - starttime

If you don't need to use elapsedtime in the loop, just inline the calculation:

while time.time() - starttime < 10:
    print("inside bottom of local while", int(time.time() - starttime))

Prune · Accepted Answer · 2017-11-22 17:04:13Z

1

You don't change elapsedtime inside the loop ... it's stuck at 0. Indent the last line:

if 1 == 0: #Change this to run either loop. See if remote or local has precidence. 
    while(elapsedtime < 10):
        print("Inside remote while  " + time.strftime("%H:%M:%S")) #Time check
        elapsedtime = time.time() - starttime #Calculate elasped time.
else:
    elapsedtime = 0
    while(elapsedtime < 10):
        print("inside bottom of local while  " + str(int(time.time() - starttime))) #Time check
        elapsedtime = time.time() - starttime #Calculate elasped time.

answered Nov 22, 2017 at 17:04

Prune

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1 Comment

Robert L. Caputo Over a year ago

Yes the indentation was the problem,

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