将日志级别设置为logging.DEBUG或logging.INFO无效

Question

I am trying to do a pretty simple logging setup. I just want all of my log output to go to the terminal and to my log file. I found the below example on Real Python that demonstrates the setup of stream and file log handlers:

# logging_example.py

import logging

# Create a custom logger
logger = logging.getLogger(__name__)

# Create handlers
c_handler = logging.StreamHandler()
f_handler = logging.FileHandler('file.log')
c_handler.setLevel(logging.WARNING)
f_handler.setLevel(logging.ERROR)

# Create formatters and add it to handlers
c_format = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
f_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
c_handler.setFormatter(c_format)
f_handler.setFormatter(f_format)

# Add handlers to the logger
logger.addHandler(c_handler)
logger.addHandler(f_handler)

logger.warning('This is a warning')
logger.error('This is an error')

## Log Output
# 2019-08-31 22:16:02,478 - __main__ - WARNING - This is a warning
# 2019-08-31 22:16:02,478 - __main__ - ERROR - This is an error

And this logs to the console and to the file as you would expect. However, when I modify the program so that it will also log INFO, like so:

import logging

# Create a custom logger
logger = logging.getLogger(__name__)

# Create handlers
c_handler = logging.StreamHandler()
f_handler = logging.FileHandler('file.log')
c_handler.setLevel(logging.DEBUG)
f_handler.setLevel(logging.DEBUG)

# Create formatters and add it to handlers
c_format = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
f_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
c_handler.setFormatter(c_format)
f_handler.setFormatter(f_format)

# Add handlers to the logger
logger.addHandler(c_handler)
logger.addHandler(f_handler)


logger.warning('logs')
logger.error('logs')
logger.info('should log but doesn\'t')
logger.debug('should log but doesn\'t')

## Log Output
# __main__ - WARNING - logs
# __main__ - ERROR - logs

What am I doing wrong? Any help would be greatly appreciated!

Answer 1

You will also need to invoke setLevel(level) on the logger object itself, as, by default, it will use ROOT 's logging level (if it doesn't have any other ancestors), which is WARNING :

logger.setLevel(logging.DEBUG)

Full code with output:

import logging

logger = logging.getLogger(__name__)

# Create handlers
c_handler = logging.StreamHandler()
f_handler = logging.FileHandler('file.log')
logger.setLevel(logging.DEBUG) # <<< Added Line
c_handler.setLevel(logging.DEBUG)
f_handler.setLevel(logging.INFO)

# Create formatters and add it to handlers
c_format = logging.Formatter('%(name)s - %(levelname)s - %(message)s')
f_format = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
c_handler.setFormatter(c_format)
f_handler.setFormatter(f_format)

# Add handlers to the logger
logger.addHandler(c_handler)
logger.addHandler(f_handler)


logger.warning('logs')
logger.error('logs')
logger.info('should log but doesn\'t')
logger.debug('should log but doesn\'t')

Output:

__main__ - WARNING - logs
__main__ - ERROR - logs
__main__ - INFO - should log but doesn't
__main__ - DEBUG - should log but doesn't

Answer 2

there is two place you can set level: Logger , Handler . both of them will affect the output of your logging setting -- in different node of the logging flow. also you can add Fliter to these two instance to filter log record with more sophisticate rule.

flowing char in the office docment make clear what happening when logging.