The below code is copied from the documentation. I am supposed to be able to see all the info logs. But I don't. I am only able to see the warn and above even though I've set setLevel to INFO.
Why is this happening? foo.py:
import logging
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')
Output:
workingDirectory$ python foo.py
warn message
error message
critical message
Where did the info and debug messages go??
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.
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.
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.
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.
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
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)>]
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.
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')
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)
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
As pointed out by #ManuelFedele, logging.basicConfig is not a good solution.
#VinaySajip explained that the setLevel is ignored because the logger is using the internal handler "of last resort", whose level is set to WARNING.
This explanation was also helpful:
The Handler.setLevel() method, just as in logger objects, specifies the lowest severity that will be dispatched to the appropriate destination. Why are there two setLevel() methods? The level set in the logger determines which severity of messages it will pass to its handlers. The level set in each handler determines which messages that handler will send on.
So a good solution is to add a handler to the logger, with the appropriate level:
import logging
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG) # or whatever level should be displayed on the console
logger.addHandler(ch)
Output
>>> logger.debug('debug message')
debug message
>>> logger.info('info message')
info message
>>> logger.warn('warn message')
<stdin>:1: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
warn message
>>> logger.error('error message')
error message
>>> logger.critical('critical message')
critical message
I can't figure out why log events are being printed to the console when I have not defined a console handler. All of the examples I read through have explicitly defined a console handler (streamhandler) in order to print messages to the console.
I want these events to be printed to a file only.
import logging
logger = logging.getLogger(__name__)
my_format = '%(asctime)-25s %(levelname)-8s LOGGER: %(name)-12s MODULE: %(module)-15s FUNCTION: %(funcName)-30s MSG: %(message)s'
my_datefmt ='%m/%d/%Y %I:%M:%S%p'
logging.basicConfig(format=my_format, datefmt=my_datefmt, level=logging.DEBUG)
formatter = logging.Formatter(my_format, datefmt=my_datefmt)
logger.setLevel(logging.DEBUG)
handler1 = logging.FileHandler('mylog.txt')
handler1.setLevel(logging.DEBUG)
handler1.setFormatter(formatter)
logger.addHandler(handler1)
logger.debug("Why is this printed to the console")
EDIT:
It has been pointed out that I was not considering the root logger. Upon calling logging.basicConfig, a default streamhandler is added to the root logger (logger = getLogger())
The root logger's handler can be modified, however I have found that I can just prevent my logger from propagating logs up to the root logger.
This can be done like so:
import logging
logger = logging.getLogger(__name__)
my_format = '%(asctime)-25s %(levelname)-8s LOGGER: %(name)-12s MODULE: %(module)-15s FUNCTION: %(funcName)-30s MSG: %(message)s'
my_datefmt ='%m/%d/%Y %I:%M:%S%p'
logging.basicConfig(format=my_format, datefmt=my_datefmt, level=logging.DEBUG)
formatter = logging.Formatter(my_format, datefmt=my_datefmt)
logger.setLevel(logging.DEBUG)
handler1 = logging.FileHandler('mylog.txt')
handler1.setLevel(logging.DEBUG)
handler1.setFormatter(formatter)
logger.addHandler(handler1)
logger.propagate = False ####
logger.debug("Why is this printed to the console")
> ipython
import logging
logging.basicConfig?
*****************logging.basicConfig**************
Signature: logging.basicConfig(**kwargs)
Docstring:
Do basic configuration for the logging system.
This function does nothing if the root logger already has handlers
configured. It is a convenience method intended for use by simple scripts
to do one-shot configuration of the logging package.
The default behaviour is to create a StreamHandler which writes to
sys.stderr, set a formatter using the BASIC_FORMAT format string, and
add the handler to the root logger.
...
You have 2 handlers.
I have a simple logging setup:
def main()
# ....
# Create logger
logging.basicConfig(filemode='w', level=logging.DEBUG)
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
# Create file handler for DEBUG and above
fh1 = logging.FileHandler(__name__ + '.debug.log')
fh1.setLevel(logging.DEBUG)
# Create file handler for INFO and above
fh2 = logging.FileHandler(__name__ + '.info.log')
fh2.setLevel(logging.INFO)
# Create console handler with INFO and above
ch = logging.StreamHandler()
ch.setLevel(logging.INFO)
# Add all the handlers to the logger
logger.addHandler(fh1)
logger.addHandler(fh2)
logger.addHandler(ch)
# ....
Then when I call
logger.info("this is an INFO message")
logger.debug("this is a DEBUG message")
I get the following on the console:
this is an INFO message
INFO:__main__:this is an INFO message
this is a DEBUG message
DEBUG:__main__:this is a DEBUG message
Even though I expected to only see INFO messages in the console (since I specified logging.info above for the StreamHandler). Why do I get these duplicates?
My .debug.log and info.log files contain only the messages at the right level, but their formatting does not include the prefices INFO:__main__ nor DEBUG:__main__. Why is their formatting different?
logging.basicConfig(filemode='w', level=logging.DEBUG)
creates a StreamHandler. So your code is creating two StreamHandlers, one with logging level DEBUG and another with level INFO.
basicConfig is a convenience function. If you want to create your own handlers, it is not necessary to call basicConfig. (Or you can call basicConfig and add additional handlers...)
If you don't supply a filename in the call to basicConfig, then a StreamHandler is added to the root logger. This is the code inside the basicConfig function:
if handlers is None:
filename = kwargs.get("filename")
if filename:
mode = kwargs.get("filemode", 'a')
h = FileHandler(filename, mode)
else:
stream = kwargs.get("stream")
h = StreamHandler(stream)
I have a problem with python's logging lib. With the code below I create a "logger":
logger = logging.getLogger()
def logger_init(level):
try:
syslog = SysLogHandler(address=LOG_DESTINATION)
except Exception, ex:
return
formatter = logging.Formatter('%(module)s[%(process)d]: %(message)s')
syslog.setFormatter(formatter)
syslog.setLevel(level)
logger.addHandler(syslog)
And I call it like:
logger.debug(SOME_STR_TO_BE_LOGGED)
OR like:
logger.error(SOME_STR_TO_BE_LOGGED)
And I initialize the logger with:
log_level = logging.ERROR
if options.DEBUG_LOG: #### This comes from options parser and it is True.
log_level = logging.DEBUG
logger_init(log_level)
The problem is that the error, and warn is working very well, but neither info nor debug methods prints anything to syslog.
I'm using syslog-ng and I designed my filter, that is it will accept every level from debug to emerg.
What is the problem here? Any ideas?
You also have to set the level of the logger, not only the handler.
Add this to your logger_init:
logger.setLevel(level)
I have setup logging as follows:
def setUp():
LOG_FORMAT = '%(asctime)s %(levelname)-8s %(name)s %(message)s'
#LOG_FORMAT = '%(asctime)s %(name)s %(message)s'
logging.basicConfig(level=logging.DEBUG, format=LOG_FORMAT)
formatter = logging.Formatter(LOG_FORMAT)
ch = logging.StreamHandler()
ch.setLevel(logging.ERROR)
ch.setFormatter(formatter)
logging.getLogger().addHandler(ch)
LOG_FILENAME = 'file.log'
fh = logging.FileHandler(LOG_FILENAME, 'w')
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)
logging.getLogger().addHandler(fh)
However, the console still shows DEBUG messages. Am I missing something here?
Note that setting the level to ERROR on fh works fine.
I think you need to remove the call to logging.basicConfig. That function adds another logging.StreamHandler that probably is the one that is printing the messages you don't want to be printed.
To check this you can take a look at the handlers attribute for the root logger (it's a list with all the handlers being used) and verify how many logging.StreamHandlers there are. Also, probably the message with level set to logging.ERROR are printed twice because of the two logging.StreamHandlers.
My final advice is avoid using logging.basicConfig if you're going to explicitly configure the handlers in the code.
Edit: Just for completeness, the source code of logging.BasicConfig is as follows:
if len(root.handlers) == 0:
filename = kwargs.get("filename")
if filename:
mode = kwargs.get("filemode", 'a')
hdlr = FileHandler(filename, mode)
else:
stream = kwargs.get("stream")
hdlr = StreamHandler(stream)
fs = kwargs.get("format", BASIC_FORMAT)
dfs = kwargs.get("datefmt", None)
fmt = Formatter(fs, dfs)
hdlr.setFormatter(fmt)
root.addHandler(hdlr)
level = kwargs.get("level")
if level is not None:
root.setLevel(level)
where you can see that unless filename is passed, a logging.StreamHandler is created.
From Python docs on logging.basicConfig:
Does basic configuration for the logging system by creating a
StreamHandler with a default Formatter and adding it to the root
logger.
As you set debug level of root logger to logging.DEBUG and you didn't switched off forwarding messages up to the root logger your DEBUG messages get logged by this StreamHandler created by basicConfig