logging module learning

Log module:

Module for printing log information.

import logging

#测试日志信息
logging.debug("debug message");

#信息日志信息
logging.info("info message");

#警告日志信息
logging.warn("warn message");

#错误日志信息
logging.error("error message");

#严重错误日志信息
logging.critical("critical message");

Only the log information level is WARNING, the logging module will print the log to the screen. (That is, only logs with a log level higher than WARNING will be output)

Log level and settings

level	When to use
DEBUG	Detailed information, which is typically of interest when debugging problems.
INFO	Prove that things are working as expected.
WARNING	Indicates that some accident has occurred, or a problem will occur in the near future (such as'disk full'). The software is still working normally.
ERROR	Due to more serious problems, the software can no longer perform some functions.
CRITICAL	A serious error indicates that the software can no longer run.

Simple configuration of the log:

import logging

#logging模块的基础设置，filename为日志打印文件（没有会创建一个文件），level为日志等级。
logging.basicConfig(filename="logger.log", level=logging.INFO)
#basicCondig的level设置的是logging的最大等级，也就是这里的等级大于INFO的都输出

logging.debug("debug message");
logging.info("info message");
logging.warn("warn message");
logging.error("error message");
logging.critical("critical message");

After the basic setting function is set, the log will not be displayed in the command box. Instead, it will be printed to a file.

Recorder, processor, filter, formatter

logger: Recorder. Log information is generated, and the interface of the application code will be displayed when there is an error.
handler: The processor. Send the log records generated by the processor to the appropriate destination.
filter: filter. Filter log information.
formatter: formatter. Specifies the log format.

The relationship between them is as follows:

Logger

The logger is a tree structure container. Before using the debug, warn, error, and critical interfaces, a Logger instance must be created. Otherwise, root logger is created, default: log level (warn), processor (StreamHandler), information is printed on the screen, formatter (default formatted output)

# 创建方法
logger = logging.getLogger(logger_name)

Modify recorder information:

logger.setLevel(logging.ERROR): Set the processor log level.
logger.addHandler(handler_name): Add a handler to the logger.
logger.removeHandler(handler_name): Remove a handler in the logger.

Handler

Common processors are:

StreamHandler
FileHandler

StreamHandler

# 创建方法
streamHandler = logging.StreamHandler(stream=None)

There are the following methods:

streamHandler.setLevel(logging.WARN): Specify the log level.
streamHandler.setFormatter(formatter_name): Set a formatter.
streamHandler.addFilter(filter_name): Add a filter.
streamHandler.removeFiltert(filter_name): Remove a filter.

FileHandler

# 创建方法
fileHandler = logging.FileHandler(filename, mode="a", encoding=None, delay=False)

Formatter

The formatter regulates the format of the output log information. It specifies the rules, format, and content of log information.

# 创建方法
formatter = logging.Formatter(fmt=None, datefmt=None)

fmt is the format string message. datefmt is the format string of the date. The default fmt uses'%(message)s', and the default datefmt uses the ISO8601 date format.

Log configuration

Explicitly create Logger, Handler and Formatter, and make related settings;
Configure in a simple way, use the basicConfig() function to configure directly;
Configure through the configuration file, use the fileConfig() function to read the configuration file;
Configure through the configuration dictionary, use the dictConfig() function to read the configuration information;
Configure through the network, use the listen() function to configure the network.

BasicConfig parameter information:

Keyword	description
filename	Create a FileHandler and use the specified file name instead of StreamHandler.
filemode	If the file name is specified, specify the mode of opening the file (if filemode is not specified, the default is'a').
format	The handler uses the specified format string.
datefmt	Use the specified date/time format.
level	Specify the level of the root logger.
stream	Use the specified stream to initialize the StreamHandler. This parameter is incompatible with'filename'. If both are present,'stream' is ignored.

Useful format

format	description
%(levelno)s	Print log level value
%(levelname)s	Print log level name
%(pathname)s	Print the path of the currently executing program
%(filename)s	Print the name of the currently executing program
%(funcName)s	Current function for printing log
%(lineno)d	Print the current line number of the log
%(asctime)s	Time to print the log
%(thread)d	Print thread id
%(threadName)s	Print thread name
%(process)d	Print process ID
%(message)s	Print log information