我认为问题在于proc.stdout中的for line语句，它在迭代整个输入之前读取它。解决方案是使用readline()代替:

#filters output
import subprocess
proc = subprocess.Popen(['python','fake_utility.py'],stdout=subprocess.PIPE)
while True:
  line = proc.stdout.readline()
  if not line:
    break
  #the real code does filtering here
  print "test:", line.rstrip()

当然，您仍然需要处理子进程的“缓冲”。

注意:根据文档，使用迭代器的解决方案应该等效于使用readline()，除了预读缓冲区，但(或正因为如此)建议的更改确实为我产生了不同的结果(Windows XP上的Python 2.5)。

实际上，如果您对迭代器进行了排序，那么缓冲现在可能是您的问题。你可以告诉子进程中的python不要缓冲它的输出。

proc = subprocess.Popen(['python','fake_utility.py'],stdout=subprocess.PIPE)

就变成了

proc = subprocess.Popen(['python','-u', 'fake_utility.py'],stdout=subprocess.PIPE)

当从python内部调用python时，我需要这个。

您需要将这些额外的参数传递给子进程。Popen:

bufsize=1, universal_newlines=True

然后可以像示例中那样进行迭代。(使用Python 3.5测试)

有点晚了，但很惊讶没有看到我认为最简单的解决方案:

import io
import subprocess

proc = subprocess.Popen(["prog", "arg"], stdout=subprocess.PIPE)
for line in io.TextIOWrapper(proc.stdout, encoding="utf-8"):  # or another encoding
    # do something with line

(这需要Python 3。)

以下对Rômulo的回答的修改适用于Python 2和3(2.7.12和3.6.1):

import os
import subprocess

process = subprocess.Popen(command, stdout=subprocess.PIPE)
while True:
  line = process.stdout.readline()
  if line != '':
    os.write(1, line)
  else:
    break

我尝试用python3，它工作，源代码

当你使用popen生成新线程时，你告诉操作系统PIPE子进程的stdout，这样父进程就可以读取它，在这里，stderr被复制到父进程的stderr。

在output_reader中，我们读取子进程的每一行stdout，方法是将它包装在迭代器中，每当有新行准备好时，迭代器就会逐行填充子进程的输出。

def output_reader(proc):
    for line in iter(proc.stdout.readline, b''):
        print('got line: {0}'.format(line.decode('utf-8')), end='')


def main():
    proc = subprocess.Popen(['python', 'fake_utility.py'],
                            stdout=subprocess.PIPE,
                            stderr=subprocess.STDOUT)

    t = threading.Thread(target=output_reader, args=(proc,))
    t.start()

    try:
        time.sleep(0.2)
        import time
        i = 0
    
        while True:
        print (hex(i)*512)
        i += 1
        time.sleep(0.5)
    finally:
        proc.terminate()
        try:
            proc.wait(timeout=0.2)
            print('== subprocess exited with rc =', proc.returncode)
        except subprocess.TimeoutExpired:
            print('subprocess did not terminate in time')
    t.join()

你也可以读行w/o循环。适用于python3.6。

import os
import subprocess

process = subprocess.Popen(command, stdout=subprocess.PIPE)
list_of_byte_strings = process.stdout.readlines()

允许逐行实时遍历stdout和stderr的函数

如果需要同时获取stdout和stderr的输出流，可以使用下面的函数。

该函数使用Queues将两个Popen管道合并到一个迭代器中。

这里我们创建了函数read_popen_pipes():

from queue import Queue, Empty
from concurrent.futures import ThreadPoolExecutor


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


def read_popen_pipes(p):

    with ThreadPoolExecutor(2) as pool:
        q_stdout, q_stderr = Queue(), Queue()

        pool.submit(enqueue_output, p.stdout, q_stdout)
        pool.submit(enqueue_output, p.stderr, q_stderr)

        while True:

            if p.poll() is not None and q_stdout.empty() and q_stderr.empty():
                break

            out_line = err_line = ''

            try:
                out_line = q_stdout.get_nowait()
            except Empty:
                pass
            try:
                err_line = q_stderr.get_nowait()
            except Empty:
                pass

            yield (out_line, err_line)

Read_popen_pipes()正在使用:

import subprocess as sp


with sp.Popen(my_cmd, stdout=sp.PIPE, stderr=sp.PIPE, text=True) as p:

    for out_line, err_line in read_popen_pipes(p):

        # Do stuff with each line, e.g.:
        print(out_line, end='')
        print(err_line, end='')

    return p.poll() # return status-code

python 3.5在subprocess模块中添加了run()和call()方法，两者都返回一个CompletedProcess对象。这样你就可以使用proc.stdout.splitlines():

proc = subprocess.run( comman, shell=True, capture_output=True, text=True, check=True )
for line in proc.stdout.splitlines():
   print "stdout:", line

请参见如何使用Subprocess Run方法在Python中执行Shell命令

我有一个问题与Popen的参数列表更新服务器，下面的代码解决了这一点。

import getpass
from subprocess import Popen, PIPE

username = 'user1'
ip = '127.0.0.1'

print ('What is the password?')
password = getpass.getpass()
cmd1 = f"""sshpass -p {password} ssh {username}@{ip}"""
cmd2 = f"""echo {password} | sudo -S apt update"""
cmd3 = " && "
cmd4 = f"""echo {password} | sudo -S apt upgrade -y"""
cmd5 = " && "
cmd6 = "exit"
commands = [cmd1, cmd2, cmd3, cmd4, cmd5, cmd6]

command = " ".join(commands)

cmd = command.split()

with Popen(cmd, stdout=PIPE, bufsize=1, universal_newlines=True) as p:
    for line in p.stdout:
        print(line, end='')

要在本地计算机上运行更新，下面的代码示例将执行此操作。

import getpass
from subprocess import Popen, PIPE

print ('What is the password?')
password = getpass.getpass()

cmd1_local = f"""apt update"""
cmd2_local = f"""apt upgrade -y"""
commands = [cmd1_local, cmd2_local]

with Popen(['echo', password], stdout=PIPE) as auth:
    for cmd in commands:
        cmd = cmd.split()
        with Popen(['sudo','-S'] + cmd, stdin=auth.stdout, stdout=PIPE, bufsize=1, universal_newlines=True) as p:
            for line in p.stdout:
                print(line, end='')