How does the Python logging setLevel function work? In the logging documentation, I found the following example:
import logging
# create logger
logger = logging.getLogger('simple_example')
logger.setLevel(logging.DEBUG)
# create console handler and set level to debug
ch = logging.StreamHandler()
ch.setLevel(logging.DEBUG)
# create formatter
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
# add formatter to ch
ch.setFormatter(formatter)
# add ch to logger
logger.addHandler(ch)
Why is it necessary to set the level to logging.DEBUG twice: once for the Logger and once for the StreamHandler? I understand that ch.setLevel(logging.DEBUG) controls the log level for the stream handler, but what is the effect of setting the level for the logger? Where does this level get reflected?
When I change the level to INFO in either the logger or the StreamHandler, I see the same output in the console. For example:
logger.setLevel(logging.INFO)
ch.setLevel(logging.DEBUG)
gives the same console output as:
logger.setLevel(logging.DEBUG)
ch.setLevel(logging.INFO)
Alright, here’s the deal with python logging setLevel. Setting the level for a logger like logger.setLevel(logging.DEBUG) essentially means you’re telling the logger to handle messages of that level and above. So if you set it to DEBUG, it will catch all messages—DEBUG, INFO, WARNING, ERROR, and CRITICAL. But, if you set it to INFO, it’ll skip anything below that level, like DEBUG messages. It’s like saying, ‘I’m only interested in things that are at least INFO level or more severe.’
So, setting the python logging setLevel is crucial because it helps filter out unnecessary logs before they reach your handlers, like StreamHandler. For example, setting logger.setLevel(logging.INFO) would mean you’re ignoring DEBUG messages and focusing on the rest.
Yeah, @joe-elmoufak’s spot on! But here’s where it gets a bit more nuanced with python logging setLevel. Think about handlers—each handler has its own logging level. So, you could have a logger set to DEBUG, but maybe you don’t want everything to appear in your console. By using StreamHandler.setLevel(logging.INFO), you’re telling the console handler to ignore DEBUG messages, even though the logger itself would be fine with them.
It’s like having a big filter at two stages: first, the logger checks if it’s worth logging at all, and then the handler decides if it’s worth showing up in the output. This means you can fine-tune where your logs go and what gets shown.
Right, so why set both levels? It’s all about flexibility and precision when you’re managing logs. For example, the python logging setLevel on the logger might be set to DEBUG, which means it’s cool with logging everything. But what if you don’t want all that data dumped into your console? This is where setting the handler level comes in. You might set the StreamHandler.setLevel(logging.ERROR) to only show error messages in the console but let everything else get saved into a file.
This way, you can have detailed logs going to files and only important, higher-severity logs being shown in real-time on the console. It’s a much cleaner way of managing logs depending on the environment or the output destination.