Python multiple loops at the same time

Question

I know that it is not possible to run multiple loops at the same time in Python. Anyhow, what I need to achieve is that I have one loop running reading loads of sensor data, every 0.25 seconds. At the same time I have signal devices running in parallel that need to send signals every 3 seconds. My question is what way is best practice to achieve this?

Does it make sense to write two scripts and run them in parallel? Does it make sense to use threading? Is there any other possibility in order to make this work?

I would be greatful for code samples.

Thank you!

Edit: Both loops are absolutely independent. So, let's say while script 1 is running, reading the sensor data, when one of the sensors received a value < 300, it should run script 2 which will send the signals. At the same time when the sensors data gets > 300 it should stop script 2.

Answer 1

"Python multiple loops at the same time. I know that it is not possible [...]" - this looks really funny.

It is possible to run two loops at the same time, exactly how you described it. And both ways make much sense, depending on what do you actually need and want. If the tasks are completely independent you should run it as two scripts. If you need those two loops to realize one task and it makes sense for them to be in one file you can use multiprocessing.

Tested for python 2.7.5+ and 3.3.2+.

Here is some minimal example:

from multiprocessing import Process
import time

def f(name):
    print('hello', name)
    time.sleep(10)

def d(name):
    print('test2', name)
    time.sleep(10)

if __name__ == '__main__':
    p1 = Process(target=f, args=('bob',))
    p2 = Process(target=d, args=('alice',))
    p1.start()
    p2.start()
    p1.join()
    p2.join()

Script runs for 10s and both strings are printed right away, which means everything works.

time python3 ./process.py 
hello bob
test2 alice

real  0m10.073s
user  0m0.040s
sys   0m0.016s

Answer 2

It is also possible by running multiple scripts and some as .pyw for convenience and having them exchange information by UDP sockets. Note 127.0.0.1 is to send to yourself under ANY circumstance. Also for port, just make sure no other programs use the port you use. As in other programs, I mean ANY program that uses ports or even basic router settings.

Sample (send)

import os
from sockets import *
host = "ip"
port = "9000"
addr = (host, port)
UDPSock = socket(AF_INET, SOCK_DGRAM)
data = "Random Text"
send = data.encode("ascii")
UDPSock.sendto(send, addr)
UDPSock.close()

Sample (Receive)

import os
from socket import *
host = ""
port = 9000
addr = (host, port)
UDPSock = socket(AF_INET, SOCK_DGRAM)
UDPSock.bind(addr)
(data, addr) = UDPSock.recvfrom(1024)#1024 is MAX bytes to receive
data = data.decode('ascii')
UDPSock.close()

You can use these to run separate loops and tell what to do from two separate programs.