When we are working on a project, we often need to log some message for easier debugging. How do we configure logging once and use it across the project?
Set up logging for the project
Suppose we have the following file in our project:
main.py module1.py module2.py
main.py is the entry point of our project and use functions or classes from
The best practice is to set up logging in
main.py like this:
import module1 import module2 import logging # other imports logging_level = logging.DEBUG main_logger = logging.getLogger() main_logger.setLevel(logging_level) # Set up a stream handler to log to the console stream_handler = logging.StreamHandler() stream_handler.setLevel(logging_level) formatter = logging.Formatter("%(name)s - %(levelname)s - %(message)s") stream_handler.setFormatter(formatter) # Add handler to logger main_logger.addHandler(stream_handler) # other codes
In the above code, we define a root logger
logging.getLogger() (notice that no name is provided to this method), and set
up the handlers and logging level properly.
module2, we only need to define a logger like this:
import logging logger = logging.getLogger(__name__) # then use logger.info() or logger.debug() in your code.
In other modules, if we define the logger using
it will automatically use the settings from the root logger. This ensures that
we only need to configure logging once in our project.
Changing logging level to disable some logging message
There is also another benefit in using a unified config: we can easily control
the logging message verbosity by changing the logging level. For example, in
the above example, we set logging level in
logging.DEBUG, so all
logger.info() message will be printed to the console. If
we do not want to see
logger.debug("xxx") messages anymore, we can set
logging level to
logging.INFO, which will disable any debug message across
the whole project.
Disable logging message from other packages
When we import 3rd party packages in our own project and set proper logging level for the project, if a logging message in 3rd party packages is above that level, the message will also be printed. Since we usually only care about logging messages in our project, we can disable logging message in 3rd party packages by setting their logger level higher or disable logging entirely for 3rd party packages. Here is the code:
import logging # suppose that the logger level of our module is logging.DEBUG, we set # logger level of other module higher than logging.DEBUG for m in ("urllib3", "foo", "bar"): logging.getLogger(m).setLevel(logging.CRITICAL) # To disable it entirely, use the following. # logging.getLogger(m).disabled = True
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