使用subprocess。避免在子程序大量输出时因buffer size满，导致父进程hang住。

subprocess-bufsize-test.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

import subprocess
from StringIO import StringIO

out = StringIO()

sp = subprocess.Popen(["python", "test_output.py"],
                      stdout=subprocess.PIPE,
                      stderr=subprocess.STDOUT)
while sp.returncode is None:
    data = sp.stdout.read()
    out.write(data)
    sp.poll()

print out.getvalue()

test_output.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

import sys

for i in range(1000):
    print "WARNING: hello jaypei from stdout ..."

for i in range(1000):
    print >> sys.stderr, "WARNING: hello jaypei from stderr ..."