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To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Variables in a loop, Newby question
Date: Fri, 27 Dec 2013 11:39:09 -0500
Organization: IISS Elusive Unicorn
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On Fri, 27 Dec 2013 00:53:43 -0800 (PST), vanommen.robert@gmail.com
declaimed the following:

>Hello everyone, I have been away for a while.
>I have been reading all the good advises and want to explain why I want to read the temperatures separately from the main script. It takes a long time to read out 10 temperatures. About 10 seconds. So that’s the reason why I had the idea to create a separate script and I thought by making te variables Global I could access them by
other scripts. Now I know that’s not the purpose of Global.
>Maybe I can create a loop that keeps running simultaneously with the rest of the script. 
>I’ve downloaded a great student book about Python and learning a lot.
>Thanks for all the answers and I’ll post more questions in the future, I’m sure of it.
>Greetings Robert

	Check the class threading.Thread, along with Queue.Queue -- presuming
the sensor reads are blocking calls, they should have minimal effect on the
main thread...

PSEUDO-code:
-=-=-=-=-
import threading
import Queue
import time

list_of_sensors = [	whatever, is, needed, to, access, each, sensor ]
#list of sensors may just be the ID strings, or if you need to open 
#each, make it a list of the opened items, so the worker doesn't 
#keep opening, reading, closing, for each sensor

tempQ = Queue.Queue()

def sensorWork(retQ, list_of_sensors):
	while True:
		for sensor in list_of_sensors:
			temp = readSensor(sensor)		#presumed to be blocking
			retQ.put((sensor, temp, time.time())
						#if a timestamp is useful

worker = threading.Thread(target=sensorWork, 
							args=(tempQ, list_of_sensors))
worker.setDaemon()	#lets it die when the main program exits

worker.start()

#now do the main processing
while True:
	#check for available temps
	numTemps = tempQ.qsize()	#should be good as only one consumer
	if numTemps > 0:
		for i in range(numTemps - 1):		
					#I'm not iterating over the queue as
					#that might starve the main process
					#if the sensor reads produce a reading
					#just fast enough to keep up with 
					#this loop
			(sensor, temp, timestamp) = tempQ.get()
			#process the temp data
	#here you do the rest of the main process, which should be
	#something that returns here at some regular interval so that
	#the loop checks for new temp readings to be processed


	
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/