日志记录，StreamHandler和标准流

Question 1

我不知道如何将信息级别的消息记录到stdout，但将其他所有内容记录到stderr。我已经阅读了http://docs.python.org/library/logging.html。有什么建议吗？

Question 2

以下脚本log1.py：

import logging, sys

class SingleLevelFilter(logging.Filter):
    def __init__(self, passlevel, reject):
        self.passlevel = passlevel
        self.reject = reject

    def filter(self, record):
        if self.reject:
            return (record.levelno != self.passlevel)
        else:
            return (record.levelno == self.passlevel)

h1 = logging.StreamHandler(sys.stdout)
f1 = SingleLevelFilter(logging.INFO, False)
h1.addFilter(f1)
rootLogger = logging.getLogger()
rootLogger.addHandler(h1)
h2 = logging.StreamHandler(sys.stderr)
f2 = SingleLevelFilter(logging.INFO, True)
h2.addFilter(f2)
rootLogger.addHandler(h2)
logger = logging.getLogger("my.logger")
logger.setLevel(logging.DEBUG)
logger.debug("A DEBUG message")
logger.info("An INFO message")
logger.warning("A WARNING message")
logger.error("An ERROR message")
logger.critical("A CRITICAL message")

运行时，产生以下结果。

C：\ temp> log1.py
调试消息
INFO消息
警告消息
错误消息
关键信息

正如你所期望的，因为终端sys.stdout和sys.stderr是相同的。现在，让我们将标准输出重定向到文件tmp：

C：\ temp> log1.py> tmp
调试消息
警告消息
错误消息
关键信息

因此，INFO消息没有被打印到终端-但指示消息sys.stderr 已被打印。让我们看一下其中的内容tmp：

C：\ temp>输入tmp
INFO消息

因此，该方法似乎可以满足您的要求。

Question 3

一般情况下，我认为是有意义的重定向报文低于WARNING到标准输出，而不是唯一的INFO消息。

基于Vinay Sajip的出色回答，我得出了以下结论：

class MaxLevelFilter(Filter):
    '''Filters (lets through) all messages with level < LEVEL'''
    def __init__(self, level):
        self.level = level

    def filter(self, record):
        return record.levelno < self.level # "<" instead of "<=": since logger.setLevel is inclusive, this should be exclusive


MIN_LEVEL= DEBUG
#...
stdout_hdlr = StreamHandler(sys.stdout)
stderr_hdlr = StreamHandler(sys.stderr)
lower_than_warning= MaxLevelFilter(WARNING)
stdout_hdlr.addFilter( lower_than_warning )     #messages lower than WARNING go to stdout
stdout_hdlr.setLevel( MIN_LEVEL )
stderr_hdlr.setLevel( max(MIN_LEVEL, WARNING) ) #messages >= WARNING ( and >= STDOUT_LOG_LEVEL ) go to stderr
#...

Question 4

由于我的编辑被拒绝，这就是我的答案。@goncalopp的回答很好，但它并不孤单，也不是开箱即用。这是我的改进版本：

import sys, logging


class LogFilter(logging.Filter):
    """Filters (lets through) all messages with level < LEVEL"""
    # http://stackoverflow.com/a/24956305/408556
    def __init__(self, level):
        self.level = level

    def filter(self, record):
        # "<" instead of "<=": since logger.setLevel is inclusive, this should
        # be exclusive
        return record.levelno < self.level

MIN_LEVEL = logging.DEBUG
stdout_hdlr = logging.StreamHandler(sys.stdout)
stderr_hdlr = logging.StreamHandler(sys.stderr)
log_filter = LogFilter(logging.WARNING)
stdout_hdlr.addFilter(log_filter)
stdout_hdlr.setLevel(MIN_LEVEL)
stderr_hdlr.setLevel(max(MIN_LEVEL, logging.WARNING))
# messages lower than WARNING go to stdout
# messages >= WARNING (and >= STDOUT_LOG_LEVEL) go to stderr

rootLogger = logging.getLogger()
rootLogger.addHandler(stdout_hdlr)
rootLogger.addHandler(stderr_hdlr)
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)

# Example Usage
>>> logger.debug("A DEBUG message")
>>> logger.info("An INFO message")
>>> logger.warning("A WARNING message")
>>> logger.error("An ERROR message")
>>> logger.critical("A CRITICAL message")

Question 5

将彩色输出发送到stderr的最简单处理程序：

class ColorStderr(logging.StreamHandler):
    def __init__(self):
        class AddColor(logging.Formatter):
            def format(self, record: logging.LogRecord):
                msg = super().format(record)
                # Green/Cyan/Yellow/Red/Redder based on log level:
                color = '\033[1;' + ('32m', '36m', '33m', '31m', '41m')[
                   min(4,int(4 * record.levelno / logging.FATAL))]
                return color + record.levelname + '\033[1;0m: ' + msg
        super().__init__(sys.stderr)
        self.setFormatter(AddColor())

用于：

logging.basicConfig(level=logging.INFO, handlers=[ColorStderr()])

或者甚至可以将格式化程序直接应用于当前的日志处理程序，而不需要ColorStderr：

logging.getLogger().handlers[0].setFormatter(AddColor())

Question 6

试试这个猴子补丁~~

import sys
import logging
import threading

def _logging_handle(self, record):
    self.STREAM_LOCKER = getattr(self, "STREAM_LOCKER", threading.RLock())
    if self.stream in (sys.stdout, sys.stderr) and record.levelname in self.FIX_LEVELS:
        try:
            self.STREAM_LOCKER.acquire()
            self.stream = sys.stdout
            self.old_handle(record)
            self.stream = sys.stderr
        finally:
            self.STREAM_LOCKER.release()
    else:
        self.old_handle(record)


def patch_logging_stream(*levels):
    """
    writing some logging level message to sys.stdout

    example:
    patch_logging_stream(logging.INFO, logging.DEBUG)
    logging.getLogger('root').setLevel(logging.DEBUG)

    logging.getLogger('root').debug('test stdout')
    logging.getLogger('root').error('test stderr')
    """
    stream_handler = logging.StreamHandler
    levels = levels or [logging.DEBUG, logging.INFO]
    stream_handler.FIX_LEVELS = [logging.getLevelName(i) for i in levels]
    if hasattr(stream_handler, "old_handle"):
        stream_handler.handle = stream_handler.old_handle
    stream_handler.old_handle = stream_handler.handle
    stream_handler.handle = _logging_handle

测试

#
patch_logging_stream(logging.INFO, logging.DEBUG)
logging.getLogger('root').setLevel(logging.DEBUG)

logging.getLogger('root').debug('test root stdout')
logging.getLogger('root').error('test root stderr')

测试输出

$ python3 test_patch_logging.py 2>/dev/null
DEBUG:root:test root stdout

$ python3 test_patch_logging.py 1>/dev/null
ERROR:root:test root stderr