如何在Python中将stdout和stderr重定向到logger

Question

我有一个记录器,有一个RotatingFileHandler.我想重定向所有Stdout与Stderr该记录器.怎么办？

Answer 1

没有足够的回复评论,但我想添加这个适用于我的版本,以防其他人处于类似的情况.

class LoggerWriter:
    def __init__(self, level):
        # self.level is really like using log.debug(message)
        # at least in my case
        self.level = level

    def write(self, message):
        # if statement reduces the amount of newlines that are
        # printed to the logger
        if message != '\n':
            self.level(message)

    def flush(self):
        # create a flush method so things can be flushed when
        # the system wants to. Not sure if simply 'printing'
        # sys.stderr is the correct way to do it, but it seemed
        # to work properly for me.
        self.level(sys.stderr)

这看起来像是这样的:

log = logging.getLogger('foobar')
sys.stdout = LoggerWriter(log.debug)
sys.stderr = LoggerWriter(log.warning)

Answer 2

如果它是一个全Python系统(即没有C库直接写入fds,正如Ignacio Vazquez-Abrams所说的那样),那么你可以使用这里建议的方法:

class LoggerWriter:
    def __init__(self, logger, level):
        self.logger = logger
        self.level = level

    def write(self, message):
        if message != '\n':
            self.logger.log(self.level, message)

然后设置sys.stdout并sys.stderr以LoggerWriter实例.

Answer 3

所有先前的答案似乎都有问题,在不需要的地方添加额外的换行符.最适合我的解决方案来自http://www.electricmonk.nl/log/2011/08/14/redirect-stdout-and-stderr-to-a-logger-in-python/,在那里他演示了如何将stdout和stderr发送到记录器:

import logging
import sys

class StreamToLogger(object):
   """
   Fake file-like stream object that redirects writes to a logger instance.
   """
   def __init__(self, logger, log_level=logging.INFO):
      self.logger = logger
      self.log_level = log_level
      self.linebuf = ''

   def write(self, buf):
      for line in buf.rstrip().splitlines():
         self.logger.log(self.log_level, line.rstrip())

logging.basicConfig(
   level=logging.DEBUG,
   format='%(asctime)s:%(levelname)s:%(name)s:%(message)s',
   filename="out.log",
   filemode='a'
)

stdout_logger = logging.getLogger('STDOUT')
sl = StreamToLogger(stdout_logger, logging.INFO)
sys.stdout = sl

stderr_logger = logging.getLogger('STDERR')
sl = StreamToLogger(stderr_logger, logging.ERROR)
sys.stderr = sl

print "Test to standard out"
raise Exception('Test to standard error')

输出如下:

2011-08-14 14:46:20,573:INFO:STDOUT:Test to standard out
2011-08-14 14:46:20,573:ERROR:STDERR:Traceback (most recent call last):
2011-08-14 14:46:20,574:ERROR:STDERR:  File "redirect.py", line 33, in 
2011-08-14 14:46:20,574:ERROR:STDERR:raise Exception('Test to standard error')
2011-08-14 14:46:20,574:ERROR:STDERR:Exception
2011-08-14 14:46:20,574:ERROR:STDERR::
2011-08-14 14:46:20,574:ERROR:STDERR:Test to standard error

请注意,self.linebuf =''是处理flush的地方,而不是实现flush函数.

Answer 4

作为 Cameron Gagnon 回应的演变，我已将LoggerWriter课程改进为：

class LoggerWriter(object):
    def __init__(self, writer):
        self._writer = writer
        self._msg = ''

    def write(self, message):
        self._msg = self._msg + message
        while '\n' in self._msg:
            pos = self._msg.find('\n')
            self._writer(self._msg[:pos])
            self._msg = self._msg[pos+1:]

    def flush(self):
        if self._msg != '':
            self._writer(self._msg)
            self._msg = ''

现在不受控制的异常看起来更好：

2018-07-31 13:20:37,482 - ERROR - Traceback (most recent call last):
2018-07-31 13:20:37,483 - ERROR -   File "mf32.py", line 317, in <module>
2018-07-31 13:20:37,485 - ERROR -     main()
2018-07-31 13:20:37,486 - ERROR -   File "mf32.py", line 289, in main
2018-07-31 13:20:37,488 - ERROR -     int('')
2018-07-31 13:20:37,489 - ERROR - ValueError: invalid literal for int() with base 10: ''

Answer 5

快速但脆弱的单线

sys.stdout.write = logger.info

sys.stderr.write = logger.error

其作用只是将记录器函数分配给 stdout/stderr 调用.write，这意味着任何写入调用都将调用记录器函数。

这种方法的缺点是，对.write记录器函数的调用通常都会添加换行符，因此您最终会在日志文件中出现额外的行，这可能会或可能不会成为问题，具体取决于您的用例。

另一个陷阱是，如果您的记录器写入 stderr 本身，我们会得到无限递归（堆栈溢出错误）。所以只能输出到文件。

Answer 6

在 Vinay Sajip 的回答中添加了flush：

class LoggerWriter:
    def __init__(self, logger, level): 
        self.logger = logger
        self.level = level 

    def write(self, message):
        if message != '\n':
            self.logger.log(self.level, message)

    def flush(self): 
        pass

Answer 7

您可以使用redirect_stdout上下文管理器:

import logging
from contextlib import redirect_stdout

logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)
logging.write = lambda msg: logging.info(msg) if msg != '\n' else None

with redirect_stdout(logging):
    print('Test')

或者像这样

import logging
from contextlib import redirect_stdout


logger = logging.getLogger('Meow')
logger.setLevel(logging.INFO)
formatter = logging.Formatter(
    fmt='[{name}] {asctime} {levelname}: {message}',
    datefmt='%m/%d/%Y %H:%M:%S',
    style='{'
)
ch = logging.StreamHandler()
ch.setLevel(logging.INFO)
ch.setFormatter(formatter)
logger.addHandler(ch)

logger.write = lambda msg: logger.info(msg) if msg != '\n' else None

with redirect_stdout(logger):
    print('Test')

Answer 8

输出重定向做对了！

问题

logger.log和其他函数（.info/ .error/etc. ）将每个调用输出为单独的行，即隐式添加（格式化和）换行符。

sys.stderr.write另一方面，只是将其文字输入写入流，包括部分行。例如：输出“ZeroDivisionError：被零除”实际上是对 4(!) 次单独调用sys.stderr.write：

sys.stderr.write('ZeroDivisionError')
sys.stderr.write(': ')
sys.stderr.write('division by zero')
sys.stderr.write('\n')

4 种最受好评的方法（1、2、3、4）因此会产生额外的换行符——只需将“1/0”放入您的程序中，您将获得以下结果：

2021-02-17 13:10:40,814 - ERROR - ZeroDivisionError
2021-02-17 13:10:40,814 - ERROR - : 
2021-02-17 13:10:40,814 - ERROR - division by zero

解决方案

将中间写入存储在缓冲区中。我使用列表作为缓冲区而不是字符串的原因是为了避免Shlemiel 画家算法。TLDR：它是 O(n) 而不是潜在的 O(n^2)

class LoggerWriter:
    def __init__(self, logfct):
        self.logfct = logfct
        self.buf = []

    def write(self, msg):
        if msg.endswith('\n'):
            self.buf.append(msg.removesuffix('\n'))
            self.logfct(''.join(self.buf))
            self.buf = []
        else:
            self.buf.append(msg)

    def flush(self):
        pass

# To access the original stdout/stderr, use sys.__stdout__/sys.__stderr__
sys.stdout = LoggerWriter(logger.info)
sys.stderr = LoggerWriter(logger.error)

2021-02-17 13:15:22,956 - ERROR - ZeroDivisionError: division by zero

对于Python 3.9以下的版本，您可以将 replace 替换.removesuffix('\n')为不太准确的.rstrip('\n').