Python Pexpect getting all output from child

Question

I am trying to get all output from child process in real time. I use spawn for creating child process but I am confused what I should send for pattern parameter in expect function. Actually I don't understand why it's not an optional parameter. I don't know if I should use send(), child doesn't need input. I'm just trying to write output to GUI. Anyway here's the code

pro=pexpect.spawn('python tx.py')
        while True:
            self.textEdit(pro.expect(['\n'])

edit: I managed to get some output

    self.pro=pexpect.spawn('python tx.py',logfile=file('mylog.txt','w'))
    self.pro.logfile_read = sys.stdout
    while(self.pro.isalive()):      
        try:
            self.textEdit.append(self.pro.read_nonblocking(size=100))
        except pexpect.TIMEOUT:
            self.pro.close(True)
        except pexpect.EOF:
            break
        time.sleep(1)           

I don't still get it. If I use read_nonblocking it still blocks main process, if I don't use it , logfile doesn't get updated so I have no output. Any idea what's wrong here?

Answer 1

If your spawned program does not need any input, then you do not need pexpect. You need the subprocess module to execute a shell process.

Read here http://docs.python.org/library/subprocess.html

Answer 2

I'll give you an example

import subprocess
import threading



def run_in_background():
   mycmd = 'ls -R /home'
   proc = subprocess.Popen(mycnd.split(), stdout=subprocess.Pipe, stderr=subprocess.STDOUT)

def run_thread():
thread = threading.Thread(target=run_in_background, args=())
thread.start()

if __name__=='__main__':
   run_in_background()

I have not tested this code, but basically this is how its done You want threading to keep your GUI from freezing, and you want subprocess to run the shell process.