stdout_output = open('testfile.txt','w')
process = subprocess.Popen(command,stdout=stdout_output,shell=True)
stdout_read = open('testfile.txt','r')
data = stdout_read.read()
print data

stdout_output = open('testfile.txt','w')
process = subprocess.Popen(command,stdout=stdout_output,shell=True)
time.sleep(3)
stdout_read = open('testfile.txt','r')
data = stdout_read.read()
print data

data = subprocess.check_output(command, shell=True)
print data

def do_stuff(proc, filename):
    # proc.poll() check if proc has ended
    while proc.poll() is None:
        print('Here you do whatever you want while you wait for the process')
        # do other stuff
        ping_pong.play()
    # here we are sure the command terminate and wrote his output
    proc.stdout.close()
    with open(filename) as f:
        return f.read()

stdout_file = open('some_file', 'w')
process = Popen(['command'], stdout=stdout_file)
output = do_stuff(process, 'some_file')

def reader(fd, finished):
    while not finished.is_set():
        data = fd.read()
        if data: print(data)
        time.sleep(SOME_TIMEOUT)

process = subprocess.Popen(command,stdout=stdout_output,shell=True)
finished = threading.Event()
reader_thread = threading.Thread(target=reader, args=(stdout_output, finished))
reader_thread.start()
process.wait()
finished.set()
reader_thread.join()

stdout_output = open('testfile.txt','w', 0)

import subprocess

"""
notifier.sh
------------------

echo "This is me"
sleep 4
echo "This is me again"

------------------
"""

command = ['bash', 'notifier.sh']
process = subprocess.Popen(command, stdout=subprocess.PIPE)

while True:
    data = process.stdout.readline()
    print data
    if 'This is me again' in data:
        break