I'm using a python script as a driver for a hydrodynamics code. When it comes time to run the simulation, I use subprocess.Popen to run the code, collect the output from stdout and stderr into a subprocess.PIPE --- then I can print (and save to a log-file) the output information, and check for any errors. The problem is, I have no idea how the code is progressing. If I run it directly from the command line, it gives me output about what iteration its at, what time, what the next time-step is, etc.

是否有一种方法既存储输出(用于日志记录和错误检查),又产生实时流输出?

我的代码的相关部分:

ret_val = subprocess.Popen( run_command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True )
output, errors = ret_val.communicate()
log_file.write(output)
print output
if( ret_val.returncode ):
    print "RUN failed\n\n%s\n\n" % (errors)
    success = False

if( errors ): log_file.write("\n\n%s\n\n" % errors)

最初,我将run_command通过tee输送,以便将副本直接发送到日志文件,流仍然直接输出到终端——但这样我就不能存储任何错误(据我所知)。


目前我的临时解决方案是:

ret_val = subprocess.Popen( run_command, stdout=log_file, stderr=subprocess.PIPE, shell=True )
while not ret_val.poll():
    log_file.flush()

然后,在另一个终端上运行tail -f log.txt (s.t. log_file = 'log.txt')。


当前回答

类似于前面的答案,但下面的解决方案适用于我在windows上使用Python3提供一个通用的方法来实时打印和登录(来源)

def print_and_log(command, logFile):
    with open(logFile, 'wb') as f:
        command = subprocess.Popen(command, stdout=subprocess.PIPE, shell=True)

        while True:
            output = command.stdout.readline()
            if not output and command.poll() is not None:
                f.close()
                break
            if output:
                f.write(output)
                print(str(output.strip(), 'utf-8'), flush=True)
        return command.poll()

其他回答

如果您能够使用第三方库,您可能能够使用像sarge这样的东西(披露:我是它的维护者)。这个库允许非阻塞地访问子流程的输出流——它是分层在子流程模块之上的。

import os

def execute(cmd, callback):
    for line in iter(os.popen(cmd).readline, ''): 
            callback(line[:-1])

execute('ls -a', print)

如果您所需要的只是输出将在控制台上可见,对我来说最简单的解决方案是将以下参数传递给Popen

with Popen(cmd, stdout=sys.stdout, stderr=sys.stderr) as proc:

哪个将使用您的python脚本stdio文件句柄

解决方案1:实时并发记录stdout和stderr

一种简单的解决方案,可以将stdout和stderr同时记录,逐行实时地记录到日志文件中。

import subprocess as sp
from concurrent.futures import ThreadPoolExecutor


def log_popen_pipe(p, stdfile):

    with open("mylog.txt", "w") as f:

        while p.poll() is None:
            f.write(stdfile.readline())
            f.flush()

        # Write the rest from the buffer
        f.write(stdfile.read())


with sp.Popen(["ls"], stdout=sp.PIPE, stderr=sp.PIPE, text=True) as p:

    with ThreadPoolExecutor(2) as pool:
        r1 = pool.submit(log_popen_pipe, p, p.stdout)
        r2 = pool.submit(log_popen_pipe, p, p.stderr)
        r1.result()
        r2.result()

解决方案2:函数read_popen_pipes(),它允许同时实时遍历两个管道(stdout/stderr)

import subprocess as sp
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()
                err_line = q_stderr.get_nowait()
            except Empty:
                pass

            yield (out_line, err_line)

# The function in use:

with sp.Popen(["ls"], stdout=sp.PIPE, stderr=sp.PIPE, text=True) as p:

    for out_line, err_line in read_popen_pipes(p):
        print(out_line, end='')
        print(err_line, end='')

    p.poll()

除了这些答案之外,一个简单的方法也可以如下:

process = subprocess.Popen(your_command, stdout=subprocess.PIPE)

while process.stdout.readable():
    line = process.stdout.readline()

    if not line:
        break

    print(line.strip())

循环可读流,只要它是可读的,如果它得到一个空的结果,停止。

这里的关键是,readline()返回一行(结尾是\n),只要有输出,如果确实在末尾,则返回空行。

希望这能帮助到一些人。