在Python中的不同线程中运行类

Question

I want to show the status on a Raspberry PI using a LED. To do this I have a program in Python that will run class methods in background using threads.

This is the code I have written:

#!/usr/bin/python

import time
import os
import threading

status = 0

class LEDStatus(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        global status
        self.current_value = None
        self.running = True 
    def run(self):
        global status

        os.system("echo gpio | sudo tee /sys/class/leds/led0/trigger")

        while True:

            for i in xrange(0, status):
                os.system("echo 1 | sudo tee /sys/class/leds/led0/brightness")

                time.sleep(0.25)

                os.system("echo 0 | sudo tee /sys/class/leds/led0/brightness")

                time.sleep(0.25)

            time.sleep(2)

        os.system("echo mmc0 | sudo tee /sys/class/leds/led0/trigger")



if __name__ == '__main__':
    leds = LEDStatus()
    try:
        leds.status = 3
        leds.start()

        while True:
            print "X"
            time.sleep(2)

    except (KeyboardInterrupt, SystemExit): #Al pulsar ctrl+c
        print "\nFinish"
        leds.running = False
        leds.join()

After the program comes to this line os.system("echo gpio | sudo tee /sys/class/leds/led0/trigger") , it doesn't execute anything in the run method.

What am I doing wrong? How can I change the value of the status variable from the main method?

Answer 1

Running sudo in os.system() call may block. It will sit there waiting for user input (the password). This depends on how sudoers file has been set up.

Your code also mixes global variables and class attributes. The status global variable is never updated, since you assign self.status = 3 instead of status = 3 .

Using global variables like this is a bit frowned upon, since you might as well really use a class attribute here. Change your __init__ to take initial status as an argument.

def __init__(self, status):
    threading.Thread.__init__(self)
    self.status = status
    self.current_value = None
    self.running = True

and in your run method use self.status :

for i in xrange(0, self.status):
    ...