Python\'s logging module lets modules or classes define their own loggers. And different loggers can have different handlers. Some of them may choose to log to a file, while som
From Logging HOWTO:
Child loggers propagate messages up to the handlers associated with their ancestor loggers. Because of this, it is unnecessary to define and configure handlers for all the loggers an application uses. It is sufficient to configure handlers for a top-level logger and create child loggers as needed. (You can, however, turn off propagation by setting the propagate attribute of a logger to False.)
Any handlers you add to the root logger will be used when child loggers create log entries.
import logging
root_handler = ...
root_logger = logging.getLogger()
root_logger.addHandler(root_handler) # Will receive all log entries
# Meanwhile in a module...
import logging
logger = logging.getLogger(__name__)
logger.error(...) # Will go to root_handler
You should probably look into the Python Logging HOWTO to understand how it works.
In short, all that modules usually do is getting a logger of the form G_LOG = logging.getLogger('package.name')
and sending messages to the logger: G_LOG.info('some message'), G_LOG.exception('something bad happened')
. Modules should not usually configure anything.
The application that uses the modules can turn the logging on and configure the handlers based on the logger names:
package
, orpackage.name
, etcThe easiest way is to configure logging through logging.basicConfig somewhere in the beginning of your application:
logging.basicConfig(level=logging.DEBUG,
format='%(asctime)s %(levelname)-8s %(message)s',
datefmt='%Y-%m-%d %H:%M:%S',
filename=log_file, filemode='a')
That way you will write all logging messages from all modules to the log_file
.
If you need a more detailed logging strategy (put logs from different loggers to different files, or send stacktraces to a separate file), it is better to define a logging config file and configure logging using logging.config.dictConfig or logging.config.fileConfig
.
P.S. I usually create two loggers as module variables:
G_LOG = logging.getLogger(__name__)
ST_LOG = logging.getLogger('stacktrace.' + __name__)
to G_LOG
I send only one-line messages. To ST_LOG
I duplicate important messages using ST_LOG.exception
which implicitly has exc_info=True
and writes the stacktrace of the current exception.
At the start of the application I load a configuration that configures two loggers (and two file handlers for them): one that receives messages that start with stacktrace
and has propagate=0
(that is stacktrace messages are not visible at the top) and the root logger that handles the rest of the messages. I will not put here my complete log config files, since it is a useful home work to understand how it all works.