Python 中 subprocess.PIPE 的非阻塞读取

我正在使用子流程模块 http://docs.python.org/library/subprocess.html启动子进程并连接到其输出流（标准输出）。我希望能够在其标准输出上执行非阻塞读取。有没有办法使 .readline 非阻塞或在调用之前检查流上是否有数据.readline？我希望它是可移植的或者至少可以在 Windows 和 Linux 下工作。

这是我现在的做法（它阻止了.readline如果没有可用数据）：

p = subprocess.Popen('myprogram.exe', stdout = subprocess.PIPE)
output_str = p.stdout.readline()

fcntl https://stackoverflow.com/questions/375427/non-blocking-read-on-a-stream-in-python/4025909#4025909, select https://stackoverflow.com/questions/375427/non-blocking-read-on-a-stream-in-python/375511#375511, asyncproc https://stackoverflow.com/questions/375427/non-blocking-read-on-a-stream-in-python/437888#437888在这种情况下没有帮助。

无论操作系统如何，无阻塞地读取流的可靠方法是使用Queue.get_nowait() https://docs.python.org/3/library/queue.html#queue.Queue.get_nowait:

import sys
from subprocess import PIPE, Popen
from threading  import Thread

try:
    from queue import Queue, Empty
except ImportError:
    from Queue import Queue, Empty  # python 2.x

ON_POSIX = 'posix' in sys.builtin_module_names

def enqueue_output(out, queue):
    for line in iter(out.readline, b''):
        queue.put(line)
    out.close()

p = Popen(['myprogram.exe'], stdout=PIPE, bufsize=1, close_fds=ON_POSIX)
q = Queue()
t = Thread(target=enqueue_output, args=(p.stdout, q))
t.daemon = True # thread dies with the program
t.start()

# ... do other things here

# read line without blocking
try:  line = q.get_nowait() # or q.get(timeout=.1)
except Empty:
    print('no output yet')
else: # got line
    # ... do something with line