Question

I am working on a project in which I want to use the command line utility cdparanoia from a python pygtk GUI. I’m using Glade for UI development. I have tried importing subprocess and using subprocess.Popen. It works, but it freezes my GUI (won’t even allow repainting of the windows) while the process is executing. Not a very nice interaction for the user. How can I prevent this behaviour? I would like put a cancel button on the window but this would work as it “freezes” the program. Ultimately, I would like to capture stderr (as below, audio info is piped to sox via stdout) and present it in as a gtk.Expander with a similar look to Synaptic when it is installing a program with the ability of the user to see things happening in real time. Also, I would like to use the text from the progress indicator (as seen below) to build a real progress indicator widget. How can I get a shell to pass info back to python in real-time rather than once the process is finished (when it gives it all as one big info dump)?

Real-time info needing captured:

Working on me - me - DISK 01.flac
cdparanoia III release 10.2 (September 11, 2008)

Ripping from sector       0 (track  1 [0:00.00])
      to sector  325195 (track 15 [1:56.70])

outputting to stdout

 (== PROGRESS == [>                             | 004727 00 ] == :-) O ==)

Here is the code I’ve used so far:

        quick = " -Z" if self.quick == True else ""
        command = "cdparanoia -w%s 1- -| sox -t wav - \"%s - %s - DISK %s%s.flac\"" %\
                    (
                        quick,
                        self.book_name.replace(" ", "_"),
                        self.author_name.replace(" ", "_"),
                        "0" if disc < 10 else "", 
                        disc
                    )
        print command
        shell = subprocess.Popen(command, shell=True, executable="/bin/bash",
                                    stdin=subprocess.PIPE,
                                    stdout=subprocess.PIPE,
                                    stderr=subprocess.PIPE
                                )
        data, err = shell.communicate(command)

With Thanks,
Narnie

Answer 1

I wrote a Python shell implementation once, and it did run wget and the actual Python console with fully functional output.

You need to use subprocess.Popen and write directly to sys.stdout:

process = subprocess.Popen(shlex.split(command), stdout = subprocess.PIPE, stderr = subprocess.STDOUT)
complete = False

while True:
  output = process.stdout.read(1)

  if output == '' and process.poll() != None:
    break

  if output != '':
    sys.stdout.write(output)
    sys.stdout.flush()