Catch output/error from sub-process ASAP

#!/usr/bin/python
#
# Runner with stdout/stderr catcher
#
from sys import argv
from subprocess import Popen, PIPE
from select import select
def __main__():
    if (len(argv) > 1) and (argv[1] == "-sub-"):
        import time, sys
        print "Application runned!"
        time.sleep(2)
        print "Slept 2 second"
        time.sleep(1)
        print "Slept 1 additional second",
        time.sleep(2)
        sys.stderr.write("Stderr output after 5 seconds")
        print "Eol on stdin"
        sys.stderr.write("Eol on stderr\n")
        time.sleep(1)
        print "Wow, we have end of work!",
    else:
        import os, io
        os.environ["PYTHONUNBUFFERED"]="1"
        p = Popen( [argv[0], "-sub-"]+argv[1:],
                   bufsize=0, # line-buffered
                   stdin=PIPE, stdout=PIPE, stderr=PIPE )
        sout = io.open(p.stdout.fileno(), 'rb', closefd=False)
        serr = io.open(p.stderr.fileno(), 'rb', closefd=False)
        while p.poll() is None:
            # App still working
            (rd, _, _) = select([p.stdout, p.stderr], [], [p.stdout, p.stderr], 1.0)
            print "select:", rd, _
            if len(rd)>0:
                for r in rd:
                    if r==p.stdout:
                        while '\n' in sout.peek(io.DEFAULT_BUFFER_SIZE):
                            line = sout.readline()
                            print "STDOUT>>", line, "<!<"
                        part_line = sout.peek(io.DEFAULT_BUFFER_SIZE)
                        if len(part_line)>0:
                            part_line = sout.read(len(part_line))
                            print "STDOUT>>", part_line, "<?<"
                    elif r==p.stderr:
                        while '\n' in serr.peek(io.DEFAULT_BUFFER_SIZE):
                            line = serr.readline()
                            print " ERROR==", line, "=!="
                        part_line = serr.peek(io.DEFAULT_BUFFER_SIZE)
                        if len(part_line)>0:
                            part_line = sout.read(len(part_line))
                            print " ERROR==", part_line, "=?="
        line = sout.read()
        if len(line)>0:
            print "STDOUT>>", line, "<-<"
        line = serr.read()
        if len(line)>0:
            print " ERROR==", line, "=-="
        print "Finish"

if __name__ == '__main__':
    __main__()