Python日志记录和子进程输出和错误流

Question

我想开始一个python进程并将子进程错误消息记录到父脚本的日志记录对象.理想情况下,我希望将日志流统一到一个文件中.我能以某种方式访问​​日志记录类的输出流吗？我所知道的一个解决方案是使用proc日志进行日志记录.如下面的答案所述,我可以从proc.stdin和stderr读取,但我有重复的日志标头.我想知道是否有办法将日志记录类下面的文件描述符直接传递给子进程？

logging.basicConfig(filename="test.log",level=logging.DEBUG)
logging.info("Started")
procLog = open(os.path.expanduser("subproc.log"), 'w')
proc = subprocess.Popen(cmdStr, shell=True, stderr=procLog, stdout=procLog)
proc.wait()
procLog.flush()

Answer 1

根据Adam Rosenfield的代码,你可以

1. 使用select.select阻塞,直到存在待读取输出 proc.stdout或proc.stderr,
2. 然后读取并记录该输出
3. 重复直到该过程完成.

请注意,以下内容将写入/tmp/test.log并运行该命令ls -laR /tmp.根据您的需求进行更改.

(PS:通常/ tmp包含普通用户无法读取的目录,因此运行ls -laR /tmp会向stdout和stderr生成输出.下面的代码在生成它们时正确地交错这两个流.)

import logging
import subprocess
import shlex
import select
import fcntl
import os
import errno
import contextlib

logger = logging.getLogger(__name__)

def make_async(fd):
    '''add the O_NONBLOCK flag to a file descriptor'''
    fcntl.fcntl(fd, fcntl.F_SETFL, fcntl.fcntl(fd, fcntl.F_GETFL) | os.O_NONBLOCK)

def read_async(fd):
    '''read some data from a file descriptor, ignoring EAGAIN errors'''
    try:
        return fd.read()
    except IOError, e:
        if e.errno != errno.EAGAIN:
            raise e
        else:
            return ''

def log_fds(fds):
    for fd in fds:
        out = read_async(fd)
        if out:
            logger.info(out)

@contextlib.contextmanager
def plain_logger():
    root = logging.getLogger()    
    hdlr = root.handlers[0]
    formatter_orig = hdlr.formatter
    hdlr.setFormatter(logging.Formatter('%(message)s'))
    yield 
    hdlr.setFormatter(formatter_orig)

def main():
    # fmt = '%(name)-12s: %(levelname)-8s %(message)s'
    logging.basicConfig(filename = '/tmp/test.log', mode = 'w',
                        level = logging.DEBUG)

    logger.info("Started")
    cmdStr = 'ls -laR /tmp'

    with plain_logger():
        proc = subprocess.Popen(shlex.split(cmdStr),
                                stdout = subprocess.PIPE, stderr = subprocess.PIPE)
        # without `make_async`, `fd.read` in `read_async` blocks.
        make_async(proc.stdout)
        make_async(proc.stderr)
        while True:
            # Wait for data to become available 
            rlist, wlist, xlist = select.select([proc.stdout, proc.stderr], [], [])
            log_fds(rlist)
            if proc.poll() is not None:
                # Corner case: check if more output was created
                # between the last call to read_async and now                
                log_fds([proc.stdout, proc.stderr])                
                break

    logger.info("Done")

if __name__ == '__main__':
    main()

编辑:

您可以重定向stdout和stderr到logfile = open('/tmp/test.log', 'a').但是,这样做的一个小难点是,任何正在写入的记录器处理程序/tmp/test.log都不会知道子进程正在编写什么,因此日志文件可能会出现乱码.

如果在子进程执行其业务时未进行日志记录调用,则唯一的问题是在子进程完成后,记录器处理程序在文件中的位置错误.这可以通过调用来解决

handler.stream.seek(0, 2)

所以处理程序将在文件末尾继续写入.

import logging
import subprocess
import contextlib
import shlex

logger = logging.getLogger(__name__)

@contextlib.contextmanager
def suspended_logger():
    root = logging.getLogger()    
    handler = root.handlers[0]
    yield 
    handler.stream.seek(0, 2)

def main():
    logging.basicConfig(filename = '/tmp/test.log', filemode = 'w',
                        level = logging.DEBUG)

    logger.info("Started")
    with suspended_logger():
        cmdStr = 'test2.py 1>>/tmp/test.log 2>&1'
        logfile = open('/tmp/test.log', 'a')
        proc = subprocess.Popen(shlex.split(cmdStr),
                                stdout = logfile,
                                stderr = logfile)
        proc.communicate()
    logger.info("Done")

if __name__ == '__main__':
    main()