日志 setLevel 被忽略

小开

Try running logging.basicConfig() in there. Of note, I see you mention INFO, but use DEBUG. As written, it should show all five messages. Swap out DEBUG with INFO, and you should see four messages.

import logging


logging.basicConfig()
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)


logger.debug('debug message')
logger.info('info message')
logger.warn('warn message')
logger.error('error message')
logger.critical('critical message')

edit: Do you have logging set up elsewhere in your code already? Can't reproduce the exact behavior you note with the specific code provided.

小开

Replace the line

logger.setLevel(logging.DEBUG)

with

logging.basicConfig(level=logging.DEBUG, format='%(message)s')

and it should work as expected. If you don't configure logging with any handlers (as in your post - you only configure a level for your logger, but no handlers anywhere), you'll get an internal handler "of last resort" which is set to output just the message (with no other formatting) at the WARNING level.

小开

This is technically also an "answer", because it can "solve" the problem. BUT I definitely DO NOT like it. It is not intuitive, and I lost 2+ hours over it.

Before:

import logging
logger = logging.getLogger('foo')
logger.setLevel(logging.INFO)
logger.info('You can not see me')
# Or you can just use the following one-liner in command line.
# $ python -c "import logging; logger = logging.getLogger('foo'); logger.setLevel(logging.INFO); logger.info('You can not see me')"

After:

import logging


logging.debug('invisible magic')  # <-- magic


logger = logging.getLogger('foo')
logger.setLevel(logging.INFO)
logger.info('But now you can see me')
# Or you can just use the following one-liner in command line.
$ python -c "import logging; logging.debug('invisible magic'); logger = logging.getLogger('foo'); logger.setLevel(logging.INFO); logger.info('But now you see me')"

PS: Comparing it to the current chosen answer, and @Vinay-Sajip's explanation, I can kind of understand why. But still, I wish it was not working that way.

小开

The accepted answer does not work for me on Win10, Python 3.7.2.

My solution:

logging.basicConfig(level=logging.DEBUG)
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)

It's order sensitive.

小开

最佳答案

As pointed by some users, using:

logging.basicConfig(level=logging.DEBUG, format='%(message)s')

like written in the accepted answer is not a good option because it sets the log level for the root logger, so it may lead to unexpected behaviours (eg. third party libraries may start to log debug messages if you set loglevel=logging.DEBUG)

In my opinion the best solution is to set log level just for your logger, like this:

import logging


logger = logging.getLogger('MyLogger')
handler = logging.StreamHandler()
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
handler.setFormatter(formatter)
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)

Not really intuitive solution, but is necessary if you want to set log level only for 'MyLogger' and leave the root logger untouched.

So, why is logging.basicConfig(level=logging.DEBUG, format='%(message)s') setting the log level globally?

Well, actually it doesn't. As said, it's just changing the configuration of the root logger and, as described in the python documentation:

Loggers should NEVER be instantiated directly, but always through the module-level function logging.getLogger(name). Multiple calls to getLogger() with the same name will always return a reference to the same Logger object.

So, logging.basicConfig is creating a StreamHandler with a default Formatter and adding it to the root logger.

The point is that if any other library is using the "root logger", you're going to set that log level for that library too so it can happen that you start to see debug logs from third party libraries.

This is why I think it's better to create your own logger and set your own formatters and handlers, so you can leave the root logger untouched.

小开

You have to set the basicConfig of the root logger to DEBUG, then you can set the level of your individual loggers to more restrictive levels.

This is not what I expected. Here is what I had to do:

#!/usr/bin/env python3


import logging
# by default this is WARNING.  Leaving it as WARNING here overrides
# whatever setLevel-ing you do later so it seems they are ignored.
logging.basicConfig(level=logging.DEBUG)


l = logging.getLogger(__name__)
l.setLevel(level=logging.INFO)
# if I hadn't called basicConfig with DEBUG level earlier,
# info messages would STILL not be shown despite calling
# setLevel above.  However now debug messages will not be shown
# for l because setLevel set it to INFO


l.warning('A warning message will be displayed')
l.info('A friendly info message will be displayed')
l.debug('A friendly debug message will not be displayed')

小开

If you want this to work WITHOUT basicConfig, you have to first set up the lowest possible level you'll log onto the logger. Since the logger sets a minimum threshold, handlers which have a lower threshold but belong to the same logger won't get those lower threshold messages since they're ignored by the logger in the first place. Intuitive, but not obvious.

We start by doing this:

lgr = logging.getLogger(name)
lgr.setLevel(logging.DEBUG)

Then, set up the handlers with the different levels you need, in my case I want DEBUG logging on stdout and INFO logging to a rotating file, so I do the following:

rot_hndlr = RotatingFileHandler('filename.log',
maxBytes=log_size,
backupCount=3)
    

rot_hndlr.setFormatter(formatter)
rot_hndlr.setLevel(logging.INFO)
lgr.addHandler(rot_hndlr)


stream_hndlr = logging.StreamHandler()
stream_hndlr.setFormatter(stream_formatter)
lgr.addHandler(stream_hndlr)

Then, to test, I do this:

lgr.debug("Hello")
lgr.info("There")

My stdout (console) will look like this:

Hello
There

and my filename.log file will look like this:

There

小开

In short, change the level in logging.basicConfig will influence the global settings. You should better set level for each logger and the specific handler in the logger.

The following is an example that displays all levels on the console and only records messages >= errors in log_file.log. Notice the level for each handler is different.

import logging
# Define logger
logger = logging.getLogger('test')


# Set level for logger
logger.setLevel(logging.DEBUG)


# Define the handler and formatter for console logging
consoleHandler = logging.StreamHandler() # Define StreamHandler
consoleHandler.setLevel(logging.DEBUG) # Set level
concolsFormatter = logging.Formatter('%(name)s - %(levelname)s - %(message)s') # Define formatter
consoleHandler.setFormatter(concolsFormatter) # Set formatter
logger.addHandler(consoleHandler) # Add handler to logger


# Define the handler and formatter for file logging
log_file = 'log_file'
fileHandler = logging.FileHandler(f'{log_file}.log') # Define FileHandler
fileHandler.setLevel(logging.ERROR) # Set level
fileFormatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s') # Define formatter
fileHandler.setFormatter(fileFormatter) # Set formatter
logger.addHandler(fileHandler) # Add handler to logger


# Test
logger.debug('This is a debug')
logger.info('This is an info')
logger.warning('This is a warning')
logger.error('This is an error')
logger.critical('This is a critical')

Console output:

# Test
test - DEBUG - This is a debug
test - INFO - This is an info
test - WARNING - This is a warning
test - ERROR - This is an error
test - CRITICAL - This is a critical

File log_file.log content:

2021-09-22 12:50:50,938 - test - ERROR - This is an error
2021-09-22 12:50:50,938 - test - CRITICAL - This is a critical

To review your logger's level:

logger.level

The result should be one of the following:

10 # DEBUG
20 # INFO
30 # WARNING
40 # ERROR
50 # CRITICAL

To review your handlers's levels:

logger.handlers

[<StreamHandler stderr (DEBUG)>,
<FileHandler ***/log_file.log (ERROR)>]

小开

Most of the answers that I've found for this issue uses the basicConfig of the root logger.

It's not helpful for those who intend to use multiple independent loggers that were not initialised with basicConfig. The use of basicConfig implies that the loglevels of ALL loggers will be changed. It also had the unfortunate side effect of generating duplicate logs.

So I tried over several days experimenting with different ways to manipulate the loglevels and came up with one that finally worked.

The trick was to not only change the log levels of all the handlers but also the all the handlers of the parent of the logger.

    def setLevel(self, infoLevel):
# To dynamically reset the loglevel, you need to also change the parent levels as well as all handlers!


self.logger.parent.setLevel(infoLevel)
for handler in self.logger.parent.handlers:
handler.setLevel(infoLevel)


self.logger.setLevel(infoLevel)
for handler in self.logger.handlers:
handler.setLevel(infoLevel)

The inspiration came from the fact that the basicConfig changes the root logger settings, so I was trying to do the same without using basicConfig.

For those that are interested, I did a little Python project on Github that illustrates the different issues with setting loglevel of the logger (it works partially), proves the SLogger (Sample Logger) implementation works, and also illustrates the duplicate log issue with basicConfig when using multiple loggers not initialised with it.

https://github.com/FrancisChung/python-logging-playground

TLDR: If you're only interested in a working sample code for the logger, the implentation is listed below

import logging


CRITICAL = 50
FATAL = CRITICAL
ERROR = 40
WARNING = 30
WARN = WARNING
INFO = 20
DEBUG = 10
NOTSET = 0




class SLogger():
"""
SLogger : Sample Logger class using the standard Python logging Library


Parameters:
name        : Name of the Logger
infoLevel   : logging level of the Logger (e.g. logging.DEBUG/INFO/WARNING/ERROR)
"""


def __init__(self, name: str, infoLevel=logging.INFO):
try:
if name is None:
raise ValueError("Name argument not specified")


logformat = '%(asctime)s %(levelname)s [%(name)s %(funcName)s] %(message)s'
self.logformat = logformat
self.name = name.upper()
self.logger = logging.getLogger(self.name)
self.logger.setLevel(infoLevel)


self.add_consolehandler(infoLevel, logformat)


except Exception as e:
if self.logger:
self.logger.error(str(e))


def error(self, message):
self.logger.error(message)


def info(self, message):
self.logger.info(message)


def warning(self, message):
self.logger.warning(message)


def debug(self, message):
self.logger.debug(message)


def critical(self, message):
self.logger.critical(message)


def setLevel(self, infoLevel):
# To dynamically reset the loglevel, you need to also change the parent levels as well as all handlers!
self.logger.parent.setLevel(infoLevel)
for handler in self.logger.parent.handlers:
handler.setLevel(infoLevel)


self.logger.setLevel(infoLevel)
for handler in self.logger.handlers:
handler.setLevel(infoLevel)


return self.logger.level


def add_consolehandler(self, infoLevel=logging.INFO,
logformat='%(asctime)s %(levelname)s [%(name)s %(funcName)s] %(message)s'):
sh = logging.StreamHandler()
sh.setLevel(infoLevel)


formatter = logging.Formatter(logformat)
sh.setFormatter(formatter)
self.logger.addHandler(sh)

小开

Create object the right way, e.g. inspired by Google:

import logging


formatter = logging.Formatter('%(asctime)s %(threadName)s: %(message)s')
log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)


handler = logging.StreamHandler()
handler.setFormatter(formatter)
log.addHandler(handler)


log.debug('debug message')
log.info('info message')
log.warn('warn message')
log.error('error message')
log.critical('critical message')

2022-11-22 23:17:59,342 MainThread: debug message
2022-11-22 23:17:59,342 MainThread: info message
2022-11-22 23:17:59,342 MainThread: warn message
2022-11-22 23:17:59,342 MainThread: error message
2022-11-22 23:17:59,342 MainThread: critical message