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python logger does not log to std out [duplicate]

I have this python code:
import logging
LOGGER = logging.getLogger(__name__)
LOGGER.info('test')
It does not get written to the console, so where does this get logged?

This does not get logged anywhere, because you did not configure any logging handlers. Without a handler configured, the log event goes nowhere. When there are no handlers configured, the root logger gets a handler automatically added if an event at WARNING or above is seen, but your event was just at INFO level.
If you put a line like this before, then you will see it logged to terminal:
logging.basicConfig(level=logging.INFO)
Basic config will add a StreamHandler writing to sys.stderr if you don't specify otherwise.

How to create a specific logger for my message?

I have spent far too much time on this and I couldn't figure out by myself.
I am writing some code that use some modules, so I want to create a specific logger for my message, not those from the other modules (they are far too many so I don't want to set a different level for each of them).
I have simplified my use case to:
import logging
logger = logging.getLogger('test')
logger.setLevel(level=logging.INFO)
print(logging.Logger.manager.loggerDict)
logger.debug('This is a debug message')
logger.info('This is an info message')
logger.warning('This is a warning message')
logger.error('This is an error message')
logger.critical('This is a critical message')
When I execute the previous code, I would expect to have my info message logged.
Instead I got:
python3 test.py
{'test': <Logger test (INFO)>}
This is a warning message
This is an error message
This is a critical message
Same with DEBUG, it always print warning/error/critical messages, not the debug/info.
If I raise the logging level (let's say ERROR), it works as expected.
python --version
Python 3.9.1

Change the configuration at the package level / root logger (documentation).
logging.basicConfig(level=logging.INFO)

Using the logging module to record the events:
import logging
#Creating an object
logger=logging.getLogger()
#Setting the threshold of logger to DEBUG
logger.setLevel(logging.DEBUG)
#Test messages
logger.debug("Debug Message")
logger.info("An information")
logger.warning("Warning")
logger.error("Error message")
logger.critical("critical Message")

Logger doesn't print debug messages after setting handler and log level

I have the following minimalist example of a logging test based on the Logging Cookbook:
import logging
logger = logging.getLogger('test')
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - '
'%(message)s')
ch.setFormatter(formatter)
logger.addHandler(ch)
print(logger.handlers)
logger.debug('hello world')
The above produces the following output:
$ python test_log.py
[<StreamHandler <stderr> (DEBUG)>]
As I've defined a handler and set the log level to debug, I was expecting the hello world log message to show up in the sample above.

If a logger's level isn't explicitly set, the system looks up the level of ancestor loggers until it gets to a logger whose level is explicitly set. In this case, it's the root logger which is the parent of the logger named 'test'. Setting the level of either this logger or the root logger to DEBUG will result in the log message being output. See this part of the documentation for the event information flow in Python logging.

So if we call logger.debug('hello world') we are generating a DEBUG event. However the logger acts as first filter before passing the event to the handlers. So if the logger level is at higher severity (like INFO) it will filter the event and the handler won't receive it, even if the event was matching the handler's level (DEBUG).
So the logger's level should be as low as the lowest level of its handlers. If you don't want the rest of the handlers to log DEBUG messages you would need to explicitly set their level higher, instead of leaving it unset and therefor inherited from the logger.

How to send celery all logs to a custom handler . in my case python-logstash handler

In my Celery application I am getting 2 types of logs on the console i.e celery application logs and task level logs (inside task I am using logger.INFO(str) syntax for logging)
I wanted to send both of them to a custom handler (in my case python-logstash handler )
For django logs I was successfull, by setting handler and logger in settings.py but I am helpless with celery

def initialize_logstash(logger=None,loglevel=logging.DEBUG, **kwargs):
# logger = logging.getLogger('celery')
handler = logstash.TCPLogstashHandler('localhost', 5959,tags=['worker'])
handler.setLevel(loglevel)
logger.addHandler(handler)
# logger.setLevel(logging.DEBUG)
return logger
from celery.signals import after_setup_task_logger
after_setup_task_logger.connect(initialize_logstash)
from celery.signals import after_setup_logger
after_setup_logger.connect(initialize_logstash)
using both after_setup_task_logger and after_setup_logger signals solved the problem

Celery provides a after_setup_logger signal that is triggered after Celery has set up the logger. Among other few arguments, the signal passes the logger object which you can add your custom logging handlers to.
from celery import signals
import logstash
import logging
#signals.after_setup_logger.connect
def setup_logstash_logger(logger, *args, **kwargs):
handler = logstash.TCPLogstashHandler('localhost', 5959)
# More logger/handler configuration
# handler.setLevel(logging.ERROR)
# ...
logger.addHandler(handler)
After fine-tuning Celery's logger you can simply rely on it to send the app messages to Logstash, even if you need to send your own messages:
logger = logging.getLogger(__name__)
logger.info('My message') # This message will also be sent to Logstash

Python - Logging from multiple modules to rotating files without printing to console

I am trying to add logging to a medium size Python project with minimal disruption. I would like to log from multiple modules to rotating files silently (without printing messages to the terminal). I have tried to modify this example and I almost have the functionality I need except for one issue.
Here is how I am attempting to configure things in my main script:
import logging
import logging.handlers
import my_module
LOG_FILE = 'logs\\logging_example_new.out'
#logging.basicConfig(level=logging.DEBUG)
# Define a Handler which writes messages to rotating log files.
handler = logging.handlers.RotatingFileHandler(LOG_FILE, maxBytes=100000, backupCount=1)
handler.setLevel(logging.DEBUG) # Set logging level.
# Create message formatter.
formatter = logging.Formatter('%(asctime)s %(name)-12s %(levelname)-8s %(message)s')
# Tell the handler to use this format
handler.setFormatter(formatter)
# Add the handler to the root logger
logging.getLogger('').addHandler(handler)
# Now, we can log to the root logger, or any other logger. First the root...
logging.debug('Root debug message.')
logging.info('Root info message.')
logging.warning('Root warning message.')
logging.error('Root error message.')
logging.critical('Root critical message.')
# Use a Logger in another module.
my_module.do_something() # Call function which logs a message.
Here is a sample of what I am trying to do in modules:
import logging
def do_something():
logger = logging.getLogger(__name__)
logger.debug('Module debug message.')
logger.info('Module info message.')
logger.warning('Module warning message.')
logger.error('Module error message.')
logger.critical('Module critical message.')
Now, here is my problem. I currently get the messages logged into rotating files silently. But I only get warning, error, and critical messages. Despite setting handler.setLevel(logging.DEBUG).
If I uncomment logging.basicConfig(level=logging.DEBUG), then I get all the messages in the log files but I also get the messages printed to the terminal.
How do I get all messages above the specified threshold to my log files without outputing them to the terminal?
Thanks!
Update:
Based on this answer, it appears that calling logging.basicConfig(level=logging.DEBUG) automatically adds a StreamHandler to the Root logger and you can remove it. When I did remove it leaving only my RotatingFileHandler, messages no longer printed to the terminal. I am still wondering why I have to use logging.basicConfig(level=logging.DEBUG) to set the message level threshold, when I am setting handler.setLevel(logging.DEBUG). If anyone can shed a little more light on these issues it would still be appreciated.

You need to call set the logging level on the logger itself as well. I believe by default, the logging level on the logger is logging.WARNING
Ex.
root_logger = logging.getLogger('')
root_logger.setLevel(logging.DEBUG)
# Add the handler to the root logger
root_logger.addHandler(handler)
The loggers log level determines what the logger will actually log (i.e what messages will actually get handed to the handlers). The handlers log level determines what it will actually handle (i.e. what messages actually are output to file, stream, etc). So you could potentially have multiple handlers attached to a logger each handling a different log level.
Here's an SO answer that explains the way this works