Logging, StreamHandler and standard streams

I can't figure out how to log info-level messages to stdout, but everything else to stderr. I already read this http://docs.python.org/library/logging.html. Any suggestion?

85279 次浏览
小开
最佳答案

The following script, 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")

when run, produces the following results.

C:\temp>log1.py
A DEBUG message
An INFO message
A WARNING message
An ERROR message
A CRITICAL message

As you'd expect, since on a terminal sys.stdout and sys.stderr are the same. Now, let's redirect stdout to a file, tmp:

C:\temp>log1.py >tmp
A DEBUG message
A WARNING message
An ERROR message
A CRITICAL message

So the INFO message has not been printed to the terminal - but the messages directed to sys.stderr have been printed. Let's look at what's in tmp:

C:\temp>type tmp
An INFO message

So that approach appears to do what you want.

小开

Generally, I think it makes sense to redirect messages lower than ABC0 to stdout, instead of only INFO messages.

Based on Vinay Sajip's excellent answer, I came up with this:

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
#...
小开

Since my edit was rejected, here's my answer. @goncalopp's answer is good but doesn't stand alone or work out of the box. Here's my improved version:

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")
小开

Try This Monkey Patch ~~

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

Test

#
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')

Test Output

$ 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
小开

Simplest handler to send colored output to stderr:

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())

Use with:

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

Or you can even apply the formatter directly to the current log handler, with no need for ColorStderr:

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

Here is my answer (combination of the others):

logger = logging.getLogger(__name__)


class LogFilter(logging.Filter):
def __init__(self, level):
self.level = level


def filter(self, record):
return record.levelno < self.level


info_handler = logging.StreamHandler(stdout)
error_handler = logging.StreamHandler(stderr)


info_handler.addFilter(LogFilter(logging.WARNING))
error_handler.setLevel(max(logging.DEBUG, logging.WARNING))


logger.handlers = [info_handler, error_handler]
logger.setLevel(logging.DEBUG)

提交答案