Common Modules (3)

logging module

The information contained in the log should be accessed by a normal program, and may be output with information such as errors, warnings, etc.

python's logging module provides a standard log interface through which you can store logs in various formats. Logging logs can be divided into five levels: debug (), info (), warning (), error (), critical ().

Eg. Simple Logging

import logging
logging.debug('debug message')
logging.info('info message')
logging.warning('warning message')
logging.error('error message')
logging.critical('critical message')
>>> WARNING:root:warning message
    ERROR:root:error message
    CRITICAL:root:critical message
# By default, the logging module prints the logs to standard output (i.e. on the screen) and displays only logs greater than or equal to the WARNING level.
# The default log level is set to WARNING (log level level CRITICAL > ERROR > WARNING > INFO > DEBUG > NOTSET)
# The default log format is log level: Logger name: user output message.

Eg. Configuration log level, log format, output location

import logging
logging.basicConfig(level=logging.DEBUG,  # Adjust the level at which the log starts to display
                    format='%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s',
                    datefmt='%a, %d %b %Y %H:%M:%S',
                    filename='test.log',  # Create log files in the current directory
                    filemode='w')  # The way to open the file is w
logging.debug('debug message')
logging.info('info message')
logging.warning('warning message')
logging.error('error message')
logging.critical('critical message')

Formatting strings that can be used in format parameters:

%(name)s       # Name of Logger
%(levelno)s    # Log level in digital form
%(levelname)s  # Log Level in Text Form
%(pathname)s   # The full path name of the module that calls the log output function may not be
%(filename)s   # File name of module calling log output function
%(module)s     # Module name for calling log output function
%(funcName)s   # Function name calling log output function
%(lineno)d     # The line of code where the statement calling the log output function is located
%(created)f    # Current time, expressed in UNIX standard floating point numbers for time
%(relativeCreated)d # The number of milliseconds since Logger was created when log information was output
%(asctime)s    # The current time in string form. The default format is "2003-07-08 16:49:45,896". Behind the comma is milliseconds.
%(thread)d     # Thread ID. Probably not.
%(threadName)s # Thread name. Probably not.
%(process)d    # Process ID. Probably not.
%(message)s    # User Output Message

Logger object: Use logger object to let files and screens output logs at the same time

import logging
logger = logging.getLogger()

# Create a handler to write to the log file
fh = logging.FileHandler('test.log')  # File Output Stream Object
# Create a handler for output to the console
ch = logging.StreamHandler()  # Standard Output Stream Object (Screen Output)

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')

fh.setFormatter(formatter)  # Get the standard format for output
ch.setFormatter(formatter)  # Get the standard format for output

logger.addHandler(fh)  # logger objects can add multiple fh and ch objects
logger.addHandler(ch)

logger.setLevel(logging.DEBUG) # Setting the level of the log

# Finally, set up the different information that the log wants to record
logger.debug('logger debug message')
logger.info('logger info message')
logger.warning('logger warning message')
logger.error('logger error message')
logger.critical('logger critical message')