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

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

其他回答

我们也可以使用默认的文件迭代器来读取stdout,而不是使用iter构造readline()。

import subprocess
import sys

process = subprocess.Popen(
    your_command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT
)
for line in process.stdout:
    sys.stdout.write(line)

Here is a class which I'm using in one of my projects. It redirects output of a subprocess to the log. At first I tried simply overwriting the write-method but that doesn't work as the subprocess will never call it (redirection happens on filedescriptor level). So I'm using my own pipe, similar to how it's done in the subprocess-module. This has the advantage of encapsulating all logging/printing logic in the adapter and you can simply pass instances of the logger to Popen: subprocess.Popen("/path/to/binary", stderr = LogAdapter("foo"))

class LogAdapter(threading.Thread):

    def __init__(self, logname, level = logging.INFO):
        super().__init__()
        self.log = logging.getLogger(logname)
        self.readpipe, self.writepipe = os.pipe()

        logFunctions = {
            logging.DEBUG: self.log.debug,
            logging.INFO: self.log.info,
            logging.WARN: self.log.warn,
            logging.ERROR: self.log.warn,
        }

        try:
            self.logFunction = logFunctions[level]
        except KeyError:
            self.logFunction = self.log.info

    def fileno(self):
        #when fileno is called this indicates the subprocess is about to fork => start thread
        self.start()
        return self.writepipe

    def finished(self):
       """If the write-filedescriptor is not closed this thread will
       prevent the whole program from exiting. You can use this method
       to clean up after the subprocess has terminated."""
       os.close(self.writepipe)

    def run(self):
        inputFile = os.fdopen(self.readpipe)

        while True:
            line = inputFile.readline()

            if len(line) == 0:
                #no new data was added
                break

            self.logFunction(line.strip())

如果您不需要日志记录,而只是想使用print(),显然可以删除大部分代码并使类更短。你也可以通过__enter__和__exit__方法来扩展它,并在__exit__中调用finished,这样你就可以很容易地将它用作上下文。

import os

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

execute('ls -a', print)

看起来行缓冲输出对您来说是可行的,在这种情况下,下面的代码可能适合您。(注意:它未经测试。)这只会实时给出子进程的标准输出。如果您希望实时同时拥有stderr和stdout,则必须使用select执行更复杂的操作。

proc = subprocess.Popen(run_command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)
while proc.poll() is None:
    line = proc.stdout.readline()
    print line
    log_file.write(line + '\n')
# Might still be data on stdout at this point.  Grab any
# remainder.
for line in proc.stdout.read().split('\n'):
    print line
    log_file.write(line + '\n')
# Do whatever you want with proc.stderr here...

为什么不直接将stdout设置为sys.stdout?如果你也需要输出到日志,那么你可以简单地重写f的write方法。

import sys
import subprocess

class SuperFile(open.__class__):

    def write(self, data):
        sys.stdout.write(data)
        super(SuperFile, self).write(data)

f = SuperFile("log.txt","w+")       
process = subprocess.Popen(command, stdout=f, stderr=f)