python subprocess select 读取

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

from __future__ import absolute_import, print_function
import os
import fcntl
import select
import subprocess
from threading import Timer


def make_nonblock(fd):
    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
    fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)


class Shell(object):
    TIMEOUT_MSG = ""

    def __init__(self, cmd):
        PIPE = subprocess.PIPE
        self.proc = subprocess.Popen(
            cmd, stdout=PIPE, stdin=PIPE, stderr=PIPE, shell=True)
        make_nonblock(self.proc.stdout)
        make_nonblock(self.proc.stderr)

    def read(self, timeout=None):
        timer = None
        ret = {}
        out_ret = []
        err_ret = []
        if timeout:
            timer = Timer(timeout, self._kill_proc, [self.proc, ])
            timer.setDaemon(True)
            timer.start()
        while True:
            out = self._read(self.proc.stdout)
            err = self._read(self.proc.stderr)
            out_ret.append(out)
            err_ret.append(err)
            if self.proc.poll() is not None:
                break
        out = self._read(self.proc.stdout)
        err = self._read(self.proc.stderr)
        out_ret.append(out)
        err_ret.append(err)
        ret["out"] = "".join(out_ret)
        ret["err"] = "".join(err_ret) + self.TIMEOUT_MSG
        ret["status"] = self.proc.returncode
        if timer:
            timer.cancel()
            timer.join()
        return ret

    def _read(self, fd):
        out = ""
        if fd is None or fd.closed:
            return out
        rd, _, _ = select.select([fd], [], [], 0)
        if rd:
            out = fd.readline()
        return out

    def _kill_proc(self, proc):
        if proc:
            try:
                proc.kill()
                self.TIMEOUT_MSG = "timeout"
            except OSError:
                pass


def main():
    shell = Shell("sleep 2;ls")
    print(shell.read(1))
    shell = Shell("ls; sleep 2")
    print(shell.read(1))
    shell = Shell("ls")
    print(shell.read())

if __name__ == "__main__":
    main()