top_subprocess.py

#! /usr/bin/env python
# -*- coding: utf-8 -*-
"""
Created on 6/9/15

@author: sampfeiffer

top_subprocess.py contains...
"""
__author__ = 'sampfeiffer'

import subprocess
import threading
import Queue
import time

class AsynchronousFileReader(threading.Thread):
    def __init__(self, fd, queue):
        assert isinstance(queue, Queue.Queue)
        assert callable(fd.readline)
        threading.Thread.__init__(self)
        self._fd = fd
        self._queue = queue

    def run(self):
        '''The body of the tread: read lines and put them on the queue.'''
        for line in iter(self._fd.readline, ''):
            self._queue.put(line)

    def eof(self):
        '''Check whether there is no more content to expect.'''
        return not self.is_alive() and self._queue.empty()


if __name__ == '__main__':
    command = "top" # your hacky CAN BUS COMMAND (without grep)
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)#, shell=True)
    stdout_queue = Queue.Queue()
    stdout_reader = AsynchronousFileReader(process.stdout, stdout_queue)
    stdout_reader.start()


    # Check the queues if we received some output (until there is nothing more to get).
    while not stdout_reader.eof():
        # Show what we received from standard output.
        while not stdout_queue.empty():
            line = stdout_queue.get()
            if "python" in line: # you do your grep stuff here in python :/
                print 'Received line on standard output that contained "python": ' + str(line)

        # Sleep a bit before asking the readers again.
        time.sleep(.5)

    stdout_reader.join()
    process.stdout.close()