logging — 用 logging 库来报告状态、错误和各类信息

Logging to a File

# logging_file_example.py
import logging

LOG_FILENAME = 'logging_example.out'
logging.basicConfig(
    filename=LOG_FILENAME,
    level=logging.DEBUG,
)

logging.debug('This message should go to the log file')

with open(LOG_FILENAME, 'rt') as f:
    body = f.read()

print('FILE:')
print(body)

Rotating Log Files

# logging_rotatingfile_example.py
import glob
import logging
import logging.handlers

LOG_FILENAME = 'logging_rotatingfile_example.out'

# Set up a specific logger with our desired output level
my_logger = logging.getLogger('MyLogger')
my_logger.setLevel(logging.DEBUG)

# Add the log message handler to the logger
handler = logging.handlers.RotatingFileHandler(
    LOG_FILENAME,
    maxBytes=20,
    backupCount=5,
)
my_logger.addHandler(handler)

# Log some messages
for i in range(20):
    my_logger.debug('i = %d' % i)

# See what files are created
logfiles = glob.glob('%s*' % LOG_FILENAME)
for filename in sorted(logfiles):
    print(filename)

Verbosity Levels

# logging_level_example.py
import logging
import sys

LEVELS = {
    'debug': logging.DEBUG,
    'info': logging.INFO,
    'warning': logging.WARNING,
    'error': logging.ERROR,
    'critical': logging.CRITICAL,
}

if len(sys.argv) > 1:
    level_name = sys.argv[1]
    level = LEVELS.get(level_name, logging.NOTSET)
    logging.basicConfig(level=level)

logging.debug('This is a debug message')
logging.info('This is an info message')
logging.warning('This is a warning message')
logging.error('This is an error message')
logging.critical('This is a critical error message')

Naming Logger Instances

# logging_modules_example.py
import logging

logging.basicConfig(level=logging.WARNING)

logger1 = logging.getLogger('package1.module1')
logger2 = logging.getLogger('package2.module2')

logger1.warning('This message comes from one module')
logger2.warning('This comes from another module')

Integration with the warnings Module

# logging_capture_warnings.py
import logging
import warnings

logging.basicConfig(
    level=logging.INFO,
)

warnings.warn('This warning is not sent to the logs')

logging.captureWarnings(True)

warnings.warn('This warning is sent to the logs')