I was expecting that the following code would output both log lines
import logging
log = logging.getLogger('hello')
log.setLevel(logging.DEBUG)
print(log.getEffectiveLevel())
log.debug('debug log')
log.critical('critical log')
The output is
10
critical log
The level is correctly set to 10 (which corresponds to DEBUG) and despite this log.debug('debug log') does not output anything - why?
You haven't configured the logging system, so it's still using the defaults (level WARN for the root logger).
https://docs.python.org/3/library/logging.html#logging.basicConfig says basicConfig
Does basic configuration for the logging system by creating a StreamHandler with a default Formatter and adding it to the root logger.
Configuring the logging system with basicConfig first will create a handler and formatter that your logger will use:
logging.basicConfig()
log = logging.getLogger('hello')
log.setLevel(logging.DEBUG)
print(log.getEffectiveLevel())
log.debug('debug log')
log.critical('critical log')
Outputs:
10
DEBUG:hello:debug log
CRITICAL:hello:critical log
In Logger.callHandlers, each handler compares the log record's level with its level. If there aren't any handlers, it will use the default of WARNING.
log output is still driven by the default WARNING level despite being effectively set to DEBUG?
print('handlers=', logging.getLogger().handlers) with and without basicConfig. The docs on Handler (docs.python.org/3/library/logging.html#logging.Handler) show that the __init__(level=NOTSET) method takes a level parameter.
WARNING. Documented here: docs.python.org/3/library/…With a StreamHandler it will
sends logging output to streams such as sys.stdout, sys.stderr or any file-like object"
according to the documentation
import logging
import sys
# Initialize Logger and set Level to DEBUG
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
# Initialize a Handler to print to stdout
handler = logging.StreamHandler(sys.stdout)
# Format Handler output
logFormatter = logging.Formatter(
"%(asctime)s %(message)s", datefmt="%m/%d/%Y %I:%M:%S %p"
)
handler.setFormatter(logFormatter)
# Set Handler Level to DEBUG
handler.setLevel(logging.DEBUG)
logger.addHandler(handler)
logger.debug('Debug Info')
>>> 09/19/2020 09:01:00 PM Debug Info
You need to add stream handler
import logging
log = logging.getLogger('hello')
log.setLevel(logging.DEBUG)
# # Create a file handler to store the logs
file_handler = logging.FileHandler('test.log')
log.addHandler(file_handler)
# # Send output to terminal
stream_handler = logging.StreamHandler()
log.addHandler(stream_handler)
log.debug('debug log')
stdoutorstderr?.setLevel()?