I must be overlooking something terribly obvious. I need to execute a C program, display its output in real time and finally parse its last line, which should be straightforward as the last line printed is always the same.

process = subprocess.Popen(args, shell = True,  
                           stdout = subprocess.PIPE, stderr = subprocess.PIPE)

# None indicates that the process hasn't terminated yet.
while process.poll() is None:

    # Always save the last non-emtpy line that was output by the child
    # process, as it will write an empty line when closing its stdout.
    out = process.stdout.readline()
    if out:
        last_non_empty_line = out

    if verbose:
        sys.stdout.write(out)   
        sys.stdout.flush()

# Parse 'out' here...

Once in a while, however, the last line is not printed. The default value for Popens's bufsize is 0, so it is supposed to be unbuffered. I have also tried, to no avail, adding fflush(stdout) to the C code just before exiting, but it seems that there is absolutely no need to flush a stream before exiting a program.

Ideas anyone?