It seems recently there were some changes of python logging package. Some code work previously doesn't work now. And I am confused. My python version is Python 2.7.15.
The first example I don't understand is that below only prints "WARNING:root:hello from warn". If I understand correctly, "logging.info" actually calls the root logger, and root logger default to warn level. So the first "hello from info" is ignored, which is fine. But why the second "hello from info" is also not printed?
import logging
logging.info("hello from info")
logging.warn("hello from warn")
logging.basicConfig(level=logging.INFO)
logging.info("hello from info")
The second question is the logging level of Handler versus logger. If we set the log level for both the handler and logger, which one is working? Or what if we just set level for Handler? Take the example as below. We already set the log level for StreamHandler, but the "hello from info" is not printed to stdout. Only the "hello from warn" (Besides, it is not "WARNING:t:hello from warn"). Why is that?
import logging
ch = logging.StreamHandler()
ch.setLevel(logging.INFO)
logger = logging.getLogger('t')
logger.addHandler(ch)
logger.info("hello from info")
logger.warn("hello from warn")
But why the second "hello from info" is also not printed?
Because
logging.info / warn / error / debug call logging.basicConfig under the hood. Example:
def info(msg, *args, **kwargs):
if len(root.handlers) == 0:
basicConfig()
root.info(msg, *args, **kwargs)
logging.basicConfig does not do anything if the root logger is already configured. Quote from the docs:
This function does nothing if the root logger already has handlers configured for it.
So, in your code, the root logger is configured with WARN level when logging.info("hello from info") is executed. The subsequent call of logging.basicConfig(level=logging.INFO) has no effect.
Rule of thumb: configure the loggers (no matter if manually or via logging.basicConfig()) as early as possible in your code.
If we set the log level for both the handler and logger, which one is working?
Both! Logger level and handler level are two different stages of filtering records. The logger level defines what records are actually passed to its handlers, while the handler level defines what records will be handled by the particular handler. Examples:
logger.setLevel(logging.INFO)
handler.setLevel(logging.ERROR)
logger.addHandler(handler)
logger.info('spam')
Since logger has level INFO, it will process spam record and pass it to its handlers. However, handler has level ERROR, so the record will not be processed by handler.
logger.setLevel(logging.WARN)
handler.setLevel(logging.DEBUG)
logger.addHandler(handler)
logger.info('spam')
Now the handler will process almost any record, including spam record since its level is INFO, thus greater than DEBUG. However, the handler will never receive spam to process because the logger will not process it, thus not passing spam to its handlers.
logger.setLevel(logging.INFO)
h1 = logging.StreamHandler()
h1.setLevel(logging.CRITICAL)
h2 = logging.FileHandler('some.log')
h2.setLevel(logging.DEBUG)
logger.addHandler(h1)
logger.addHandler(h2)
logger.info('spam')
Now the logger has two handlers, h1 printing records to terminal, h2 writing them to file. The logger will pass only records of level INFO or greater to its handlers. However, you will see only records with level CRITICAL in terminal, but all records in log file.
Related
I have a Python script and I want that the info method write the messages in the console. But the warning, critical or error writes the messages to a file. How can I do that?
I tried this:
import logging
console_log = logging.getLogger("CONSOLE")
console_log.setLevel(logging.INFO)
stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging.INFO)
console_log.addHandler(stream_handler)
file_log = logging.getLogger("FILE")
file_log.setLevel(logging.WARNING)
file_handler = logging.FileHandler('log.txt')
file_handler.setLevel(logging.WARNING)
file_log.addHandler(file_handler)
def log_to_console(message):
console_log.info(message)
def log_to_file(message):
file_log.warning(message)
log_to_console("THIS SHOULD SHOW ONLY IN CONSOLE")
log_to_file("THIS SHOULD SHOW ONLY IN FILE")
but the message that should be only in the file is going to the console too, and the message that should be in the console, is duplicating. What am I doing wrong here?
What happens is that the two loggers you created propagated the log upwards to the root logger. The root logger does not have any handlers by default, but will use the lastResort handler if needed:
A "handler of last resort" is available through this attribute. This
is a StreamHandler writing to sys.stderr with a level of WARNING, and
is used to handle logging events in the absence of any logging
configuration. The end result is to just print the message to
sys.stderr.
Source from the Python documentation.
Inside the Python source code, you can see where the call is done.
Therefore, to solve your problem, you could set the console_log and file_log loggers' propagate attribute to False.
On another note, I think you should refrain from instantiating several loggers for you use case. Just use one custom logger with 2 different handlers that will each log to a different destination.
Create a custom StreamHandler to log only the specified level:
import logging
class MyStreamHandler(logging.StreamHandler):
def emit(self, record):
if record.levelno == self.level:
# this ensures this handler will print only for the specified level
super().emit(record)
Then, use it:
my_custom_logger = logging.getLogger("foobar")
my_custom_logger.propagate = False
my_custom_logger.setLevel(logging.INFO)
stream_handler = MyStreamHandler()
stream_handler.setLevel(logging.INFO)
file_handler = logging.FileHandler("log.txt")
file_handler.setLevel(logging.WARNING)
my_custom_logger.addHandler(stream_handler)
my_custom_logger.addHandler(file_handler)
my_custom_logger.info("THIS SHOULD SHOW ONLY IN CONSOLE")
my_custom_logger.warning("THIS SHOULD SHOW ONLY IN FILE")
And it works without duplicate and without misplaced log.
When I run the below piece of code, the logging is working fine. But when I comment #1) and #2) under setup_logger the log is not displayed.
What does #1) and #2) do here?
import logging
import sys
def get_logger(name):
print('get_logger -- ', name)
log = logging.getLogger("hello.{}".format(name))
return log
def setup_logger():
print('setup_logger')
root = logging.getLogger("")
root.setLevel(logging.ERROR)
handler = logging.StreamHandler(sys.stdout)
handler.setFormatter(logging.Formatter(
fmt="%(asctime)s - %(name)s - %(levelname)s - %(message)s"
))
root.addHandler(handler)
logger = logging.getLogger("hello") #1
logger.setLevel(logging.DEBUG) #2
LOG = get_logger(__name__)
setup_logger()
print(LOG)
def main():
LOG.debug('hello')
if __name__ == '__main__':
main()
The first line you marked gets a logger with given name. If there currently is no logger with the name you provided, a new one will be created (Also known as Singleton). You can read more about logging.getLogger in the Python documentation :
Return a logger with the specified name or, if name is None, return a logger
which is the root logger of the hierarchy. If
specified, the name is typically a dot-separated hierarchical name
like ‘a’, ‘a.b’ or ‘a.b.c.d’. Choice of these names is entirely up to
the developer who is using logging.
All calls to this function with a given name return the same logger instance.
This means that logger instances never need to be
passed between different parts of an application.
The second line you marked sets the loglevel on the logger instance. If you set the loglevel to DEBUG, all messages you log will be printed to the console / file. If you set it to INFO, all messages except for
debug messages will be logged. And so on. Quote from the docs again:
Sets the threshold for this logger to level. Logging messages which
are less severe than level will be ignored; logging messages which
have severity level or higher will be emitted by whichever handler or
handlers service this logger, unless a handler’s level has been set to
a higher severity level than level.
When a logger is created, the level is set to NOTSET (which causes all
messages to be processed when the logger is the root logger, or
delegation to the parent when the logger is a non-root logger). Note
that the root logger is created with level WARNING.
If you still have questions, I can edit my post to answer them.
Overview
I want to use httpimport as a logging library common to several scripts. This module generates logs of its own which I do not know how to silence.
In other cases such as this one, I would have used
logging.getLogger('httpimport').setLevel(logging.ERROR)
but it did not work.
Details
The following code is a stub of the "common logging code" mentioned above:
# toconsole.py
import logging
import os
log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s %(message)s')
handler_console = logging.StreamHandler()
level = logging.DEBUG if 'DEV' in os.environ else logging.INFO
handler_console.setLevel(level)
handler_console.setFormatter(formatter)
log.addHandler(handler_console)
# disable httpimport logging except for errors+
logging.getLogger('httpimport').setLevel(logging.ERROR)
A simple usage such as
import httpimport
httpimport.INSECURE = True
with httpimport.remote_repo(['githublogging'], 'http://localhost:8000/') :
from toconsole import log
log.info('yay!')
gives the following output
[!] Using non HTTPS URLs ('http://localhost:8000//') can be a security hazard!
2019-08-25 13:56:48,671 yay!
yay!
The second (bare) yay! must be coming from httpimport, namely from its logging setup.
How can I disable the logging for such a module, or better - raise its level so that only errors+ are logged?
Note: this question was initially asked at the Issues section of the GitHub repository for httpimport but the author did not know either how to fix that.
Author of httpimport here.
I totally forgot I was using the basicConfig logger thing.
It is fixed in master right now (0.7.2) - will be included in next PyPI release:
https://github.com/operatorequals/httpimport/commit/ff2896c8f666c3f16b0f27716c732d68be018ef7
The reason why this is happening is because when you do import httpimport they do the initial configuration for the logging machinery. This happens right here. What this means is that the root logger already has a StreamHandler attached to it. Because of this, and the fact that all loggers inherit from the root logger, when you do log.info('yay') it not only uses your Handler and Formatter, but it also propagates all they way to the root logger, which also emits the message.
Remember that whoever calls basicConfig first when an application starts that sets up the default configuration for the root logger, which in turn, is inherited by all loggers, unless otherwise specified.
If you have a complex logging configuration you need to ensure that you call it before you do any third-party imports which might call basicConfig. basicConfig is idempotent meaning the first call seals the deal, and subsequent calls have no effect.
Solutions
You could do log.propagate = False and you will see that the 2nd yay will not show.
You could attach the Formatter directly to the already existent root Handler by doing something like this (without adding another Handler yourself)
root = logging.getLogger('')
formatter = logging.Formatter('%(asctime)s %(message)s')
root_handler = root.handlers[0]
root_handler.setFormatter(formatter)
You could do a basicConfig call when you initialize your application (if you had such a config available, with initial Formatters and Handlers, etc. that will elegantly attach everything to the root logger neatly) and then you would only do something like logger = logging.getLogger(__name__) and logger.info('some message') that would work the way you'd expect because it would propagate all the way to the root logger which already has your configuration.
You could remove the initial Handler that's present on the root logger by doing something like
root = logging.getLogger('')
root.handlers = []
... and many more solutions, but you get the idea.
Also do note that logging.getLogger('httpimport').setLevel(logging.ERROR) this works perfectly fine. No messages below logging.ERROR would be logged by that logger, it's just that the problem wasn't from there.
If you however want to completely disable a logger you can just do logger.disabled = True (also do note, again, that the problem wasn't from the httpimport logger, as aforementioned)
One example demonstrated
Change your toconsole.py with this and you won't see the second yay.
import logging
import os
log = logging.getLogger(__name__)
log.setLevel(logging.DEBUG)
root_logger = logging.getLogger('')
root_handler = root_logger.handlers[0]
formatter = logging.Formatter('%(asctime)s %(message)s')
root_handler.setFormatter(formatter)
# or you could just keep your old code and just add log.propagate = False
# or any of the above solutions and it would work
logging.getLogger('httpimport').setLevel(logging.ERROR)
I created the following script. Could any of you explain to me why the output is like what shows below
Source
import logging
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
print('debug', logger.isEnabledFor(logging.DEBUG))
print('info', logger.isEnabledFor(logging.INFO))
print('warning', logger.isEnabledFor(logging.WARNING))
print('error', logger.isEnabledFor(logging.ERROR))
logger.debug('debug')
logger.info('info')
logger.warning('warning')
logger.error('error')
logging.debug('debug')
logging.info('info')
logging.warning('warning')
logging.error('error')
Output
debug True
info True
warning True
error True
warning
error
DEBUG:root:debug
INFO:root:info
WARNING:root:warning
ERROR:root:error
Specifically
what is the difference between logger.info and logging.info here
how come that logger.isEnabledFor(logging.DEBUG) is True while logger.debug('debug') does not show anything
how come that logger.info has no output but logging.info has
A few things to clarify:
Default log level for root logger is WARNING
Root logger is not initialized if you do nothing, that is, without any handlers or formatter set up:
>>> import logging
>>> logging.root.handlers
[]
Okay, but you found out the problem: when logging level set to DEBUG, the root logger is not working as expected. Debug messages are ignored. With the same not configured root logger, warning messages output normally. Why is that?
Keep in mind we don't have any handler for root logger right now. But looking into the code, we do see:
if (found == 0):
if lastResort:
if record.levelno >= lastResort.level:
lastResort.handle(record)
elif raiseExceptions and not self.manager.emittedNoHandlerWarning:
sys.stderr.write("No handlers could be found for logger"
" \"%s\"\n" % self.name)
self.manager.emittedNoHandlerWarning = True
Which means, we have a lastResort for backup if no handler is found. You can refer to the definition of lastResort, it is initialized with logging level WARNING. Meanwhile, debug messages don't have this backup so they are ignored when no handler is set.
For your questions:
These two loggers are identical, since the root logger is returned when getLogger() receives no arguments.
See below:
Logger.isEnabledFor(lvl)
Indicates if a message of severity lvl would
be processed by this logger. This method checks first the module-level
level set by logging.disable(lvl) and then the logger’s effective
level as determined by getEffectiveLevel().
Calling any logging functions in logging module will initialize the root logger with basicConfig() which adds a default handler, so that the subsequent calls on logger will also work.
What you should do is, use logging.basicConfig() to set up a default handler for root logger and messages will be output according to the logger level and message level.
getLogger creates an instance of Logger class if argument name is added. Otherwise it returns root logger. So in this case the program is using the common logger as functions logging.debug, logging.info, logging.warning, logging.info
Is there anything in this code that would explain why my info messages aren't going into the log. Properly formatted warnings and above are going into both log files.
Initializing logger:
logger = logging.getLogger()
f = logging.Formatter('%(asctime)s\n%(levelname)s: %(funcName)s %(message)s')
out = logging.handlers.RotatingFileHandler(filename=self.f_stdout, maxBytes=1048576, backupCount=99)
err = logging.handlers.RotatingFileHandler(filename=self.f_stderr, maxBytes=1048576, backupCount=99)
out.setLevel(logging.INFO)
err.setLevel(logging.WARNING)
err.setFormatter(f)
logger.addHandler(out)
logger.addHandler(err)
Usage:
logging.info('this doesnt get logged')
logging.warning('this gets logged to stdout and stderr with respective formatting')
You never actually set the log level of the root logger object itself (the logger variable in your code). Both handlers and loggers have log levels; lines only reach the output if they're above both thresholds.
Since you don't set the root log level, it uses its default (warning). Try adding a call to logger.setLevel(logging.INFO) to change that.