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1 logging 日志级别

级别	级别数量	使用场合
DEBUG	10	详细信息，常用语调试
INFO	20	程序正常运行过程中产生的一些信息
WARNING	20	警告用户，虽然程序还在正常工作，但有可能发生错误
ERROR	40	由于更严重的问题，程序已不能执行一些功能了
CRITICAL	50	严重错误，程序已不能继续运行了

2 logging 默认的是warning级别

import logging
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")

执行结果如下：

WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

3 可以通过logging.basicConfig(level=logging.DEBUG) 来设置日志级别

import logging
logging.basicConfig(level=logging.DEBUG)
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")

运行结果如下：

DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

4 logging日志是一部写入的，logging打印的内容和print打印的内筒先后顺序是不一致的

import logging
print("this is print log")
logging.basicConfig(level=logging.DEBUG)
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")

运行结果有可能是下面这种输出顺序

DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log
this is print log

5 logging.basicConfig(filename=”demo.log”)可以指定日志文件名，默认在当前目录下生成文件，此时不再往屏幕打印日志，而是将日志信息输出到指定的日志文件中去

import logging
print("this is print log")
logging.basicConfig(filename="demo.log",level=logging.DEBUG)
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")

运行后屏幕上输出结果为：

this is print log

而在当前文件下生成了一个demo.log的日志文件，此日志文件的内容为：

DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

6 logging.basicConfig(filemode=’w’) 可以指定日志文件的模式，w表示每次清空日志文件，重新写入，a表示在日志文件后面追加，默认的模式为a

将上述 5 中的实例代码再执行一次，demo.log中内容为：

DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log
DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

若代码修改为如下，再执行：

import logging
print("this is print log")
logging.basicConfig(filename="demo.log",filemode='w',level=logging.DEBUG)
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")

运行后，demo.log中的内容又恢复到如下内容：

DEBUG:root:this is debug log
INFO:root:this is info log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

7 logging 向日志中写入变量的方式

import logging
logging.basicConfig(level=logging.DEBUG)
name="zhangsan"
age=20
logging.debug("name: %s age: %d",name,age)
logging.info("name: %s age: %d" %(name,age))
logging.warning("name: {} age: {}".format(name,age))
logging.error("name: {name} age: {age}".format(name=name,age=age))

运行结果如下：

DEBUG:root:name: zhangsan age: 20
INFO:root:name: zhangsan age: 20
WARNING:root:name: zhangsan age: 20
ERROR:root:name: zhangsan age: 20

8 日志内容格式增加一些公共的内容

import logging
logging.basicConfig(format=("%(asctime)s | %(levelname)s | %(filename)s:%(lineno)s | %(message)s"),
                    datefmt="%Y-%m-%d_%H:%M:%S",
                    level=logging.DEBUG)
name="zhangsan"
age=20
logging.debug("name: %s age: %d",name,age)
logging.info("name: %s age: %d" %(name,age))
logging.warning("name: {} age: {}".format(name,age))
logging.error("name: {name} age: {age}".format(name=name,age=age))

运行结果为：

2020-08-03_07:20:42 | DEBUG | test1.py:9 | name: zhangsan age: 20
2020-08-03_07:20:42 | INFO | test1.py:10 | name: zhangsan age: 20
2020-08-03_07:20:42 | WARNING | test1.py:11 | name: zhangsan age: 20
2020-08-03_07:20:42 | ERROR | test1.py:12 | name: zhangsan age: 20

9 logging的高级应用

logging模块采用了模块化设计，主要包含四种组件

Loggers：记录器，提供应用程序代码能直接使用的接口
Handlers：处理器，将记录器产生的日志发送到目的地
Filters：过滤器，提供更好的粒度控制，决定哪些日志会被输出
格式化器：设置内置内容的组成结构和消息字段

10 logging的高级应用流程


                             |---创建屏幕StreamHandler--设置日志等级---|
创建一个logger并设置默认等级---|                                       |----创建formatter----用formatter渲染所有的hansdler----将所有的handler加入logger内----程序调用logger
                             |---创建文件FileHandler--设置日志等级-----|

11 loggers记录器

提供应用程序的调用接口

logger=logging。getLogger(name)
logger是单例的
决定日志记录的级别

logger.setLevel()
将日志内容传递到相关联的handlers中

logger.addHandler()

logger。removeHandler()

12 handler处理器

StreamHandler

标准输出stdout（如显示器）分发器

创建方法： sh=logging.StreamHandler(stream=None)
FileHandler

将日志保存到磁盘文件的处理器

创建方法：fh=logging.FileHandler(filename,mode=”a”,enconding=None,delay=False)
setFormatter(): 设置当前handler对象使用的消息格斯

13 常用的Handlers处理器

StreamHandler
FileHandler
BaseRotatingHandler
RotatingHandler
TimedRotatingFileHandler
SocketHandler
DatagramHandler
SMTPHandler
SysLogHandler
NTEventLogHandler
HTTPHandler
WatchedFileHandler
QueueHandler
NullHandler

14 常见的formatter格式

属性	格式	描述
asctime	%(asctime)s	日志产生的时间，默认格式为2020-08-03 12.12.12,265
created	%(created)f	time.time()生成的日志创建时间戳
filename	%(filename)s	生成日志的程序名
funcName	%(funcName)s	调用日志的函数名
levelname	%(levelname)s	日志级别（DEBUG,INFO,WARNING,ERROR,CRITICAL)
levelno	%(levelno)s	日志级别对应的数值
lineno	%(lineno)s)	日志所针对的代码行号（如果可用的话）
module	%(module)s	生成日志的模块名
mesecs	%(mesecs)d	日志生成的时间的毫秒部分
message	%(message)s	具体的日志信息
name	%(name)s	日志调用者
pathname	%(pathname)s	生成日志的文件的完整路径
process	%(process)d	生成日志的进程id（如果可用）
processName	%(processName)s	进程名（如果可用）
thread	%(thread)d	生成日志的线程id（如果可用）
threadName	%(threadName)s	线程名（如果可用）

15 下面两段代码的功能是完全一样的，使用logging直接调info、debug等日志与实例化一个默认的root logger是一样的，换言之，使用logging直接调日志方法的方式就是通过获取root日志来实现的

import logging
logging.debug("this is debug log")
logging.info("this is info log")
logging.warning("this is warning log")
logging.error("this is error log")
logging.critical("this is critical log")
logger=logging.getLogger()
logger.debug("this is debug log")
logger.info("this is info log")
logger.warning("this is warning log")
logger.error("this is error log")
logger.critical("this is critical log"

运行结果如下：

WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log
WARNING:root:this is warning log
ERROR:root:this is error log
CRITICAL:root:this is critical log

16 下面一段代码使用getLogger时指定一个名称，即实例化一个logger，然后设置两种处理器，分别往控制台和文件中写日志，还可以设置日志内容的格式，具体如下所示

import logging
logger=logging.getLogger("test")
console_handler=logging.StreamHandler()
console_handler.setLevel(logging.DEBUG)
file_handler=logging.FileHandler(filename="demo.log")
file_handler.setLevel(logging.DEBUG)
formatter=logging.Formatter(fmt="%(asctime)s | %(levelname)s | %(filename)s:%(lineno)s | %(message)s")
console_handler.setFormatter(formatter)
file_handler.setFormatter(formatter)
logger.addHandler(console_handler)
logger.addHandler(file_handler)
log=logger
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")

运行结果如下：

2020-08-04 23:08:56,625 | WARNING | test1.py:25 | this is warning log
2020-08-04 23:08:56,625 | ERROR | test1.py:26 | this is error log
2020-08-04 23:08:56,625 | CRITICAL | test1.py:27 | this is critical log

并且在demo.log日志文件中写入了如下内容：

2020-08-04 23:08:56,625 | WARNING | test1.py:25 | this is warning log
2020-08-04 23:08:56,625 | ERROR | test1.py:26 | this is error log
2020-08-04 23:08:56,625 | CRITICAL | test1.py:27 | this is critical log

17 上述 16 的日志打印明显与本来的期望是不一致的，本来期望控制台和文件都是设置了DEBUG级别，但实际上控制台和文件中都打印了Warning的级别的日志

这里需要注意的是，logger默认的日志级别是warning，而日志的最终级别将取决于logger和handler级别的最高级别，所以上述16中虽然控制台和文件handler的日志级别都设置了debug，但是因为logger默认级别是warning，所以最终打印的都是warning级别，下面一段代码将logger设置为debug级别，然后将控制台设置为info，将文件handler设置为warning，然后再看一下效果：

import logging
logger=logging.getLogger("test")
logger.setLevel(logging.DEBUG)
console_handler=logging.StreamHandler()
console_handler.setLevel(logging.INFO)
file_handler=logging.FileHandler(filename="demo.log")
file_handler.setLevel(logging.WARNING)
formatter=logging.Formatter(fmt="%(asctime)s | %(levelname)s | %(filename)s:%(lineno)s | %(message)s")
console_handler.setFormatter(formatter)
file_handler.setFormatter(formatter)
logger.addHandler(console_handler)
logger.addHandler(file_handler)
log=logger
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")

运行结果如下：

2020-08-04 23:21:37,888 | INFO | test1.py:25 | this is info log
2020-08-04 23:21:37,888 | WARNING | test1.py:26 | this is warning log
2020-08-04 23:21:37,888 | ERROR | test1.py:27 | this is error log
2020-08-04 23:21:37,888 | CRITICAL | test1.py:28 | this is critical log

而在demo.log日志文件中写入了如下内容，此时与上述分析一致了

2020-08-04 23:21:37,888 | WARNING | test1.py:26 | this is warning log
2020-08-04 23:21:37,888 | ERROR | test1.py:27 | this is error log
2020-08-04 23:21:37,888 | CRITICAL | test1.py:28 | this is critical log

18 定义filter并给控制台的handler加一个filter，过滤的name与日志名称不一致，如下代码，此时则不会往控制台写日志，但日志文件的日志还是正常写的

import logging
logger=logging.getLogger("test")
logger.setLevel(logging.DEBUG)
console_handler=logging.StreamHandler()
console_handler.setLevel(logging.INFO)
file_handler=logging.FileHandler(filename="demo.log")
file_handler.setLevel(logging.WARNING)
formatter=logging.Formatter(fmt="%(asctime)s | %(levelname)s | %(filename)s:%(lineno)s | %(message)s")
console_handler.setFormatter(formatter)
file_handler.setFormatter(formatter)
logger.addHandler(console_handler)
logger.addHandler(file_handler)
filter=logging.Filter("test1")
console_handler.addFilter(filter)
log=logger
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")

此时运行后控制台结果为空，日志文件如下日志打印正常

2020-08-04 23:31:00,459 | WARNING | test1.py:29 | this is warning log
2020-08-04 23:31:00,459 | ERROR | test1.py:30 | this is error log
2020-08-04 23:31:00,459 | CRITICAL | test1.py:31 | this is critical log

19 配置文件的方式

(1) 首先编写类似如下的log配置文件：logging.conf，这里面定义了root和test两个logger

[loggers]
keys=root,test
[handlers]
keys=fileHandler,consoleHandler
[formatters];
keys=simpleFormatter
[logger_root]
level=DEBUG
handlers=consoleHandler
[logger_test]
level=DEBUG
handlers=fileHandler,consoleHandler
qualname=test
propagate=0
[handler_consoleHandler]
class=StreamHandler
args=(sys.stdout,)
level=DEBUG
formatter=simpleFormatter
[handler_fileHandler]
class=handlers.TimedRotatingFileHandler
args=("test.log","midnight",1,0)
level=DEBUG
formatter=simpleFormatter
[formatter_simpleFormatter]
format=%(asctime)s|%(levelname)s|%(filename)s[line:%(lineno)d]|%(message)s
datafmt=%Y-%m-%d_%H:%M:%S

（2）然后在py文件中编写如下代码，这里演示了root的logger和test的logger两种的使用方式


import logging.config
logging.config.fileConfig("logging.conf")
logger=logging.getLogger("test")
log=logger
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")
rlog=logging.getLogger("root")
rlog.debug("this is debug log")
rlog.info("this is info log")
rlog.warning("this is warning log")
rlog.error("this is error log")
rlog.critical("this is critical log")

运行结果如下：

2020-08-05 00:25:02,673|DEBUG|test1.py[line:8]|this is debug log
2020-08-05 00:25:02,674|INFO|test1.py[line:9]|this is info log
2020-08-05 00:25:02,674|WARNING|test1.py[line:10]|this is warning log
2020-08-05 00:25:02,674|ERROR|test1.py[line:11]|this is error log
2020-08-05 00:25:02,674|CRITICAL|test1.py[line:12]|this is critical log
2020-08-05 00:25:02,674|DEBUG|test1.py[line:15]|this is debug log
2020-08-05 00:25:02,674|INFO|test1.py[line:16]|this is info log
2020-08-05 00:25:02,674|WARNING|test1.py[line:17]|this is warning log
2020-08-05 00:25:02,674|ERROR|test1.py[line:18]|this is error log
2020-08-05 00:25:02,674|CRITICAL|test1.py[line:19]|this is critical log

同时在test.log日志文件中生成如下日志：

2020-08-05 00:25:02,673|DEBUG|test1.py[line:8]|this is debug log
2020-08-05 00:25:02,674|INFO|test1.py[line:9]|this is info log
2020-08-05 00:25:02,674|WARNING|test1.py[line:10]|this is warning log
2020-08-05 00:25:02,674|ERROR|test1.py[line:11]|this is error log
2020-08-05 00:25:02,674|CRITICAL|test1.py[line:12]|this is critical log

20 在上述19的基础上，加入在其他文件中想使用建好的log系统进行日志的打印，有如下两种使用方法：

import test1
import logging
log=logging.getLogger("test")
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")
log=test1.logger
log.debug("this is debug log")
log.info("this is info log")
log.warning("this is warning log")
log.error("this is error log")
log.critical("this is critical log")

运行结果如下：

2020-08-05_00:31:35|DEBUG|test2.py[line:8]|this is debug log
2020-08-05_00:31:35|INFO|test2.py[line:9]|this is info log
2020-08-05_00:31:35|WARNING|test2.py[line:10]|this is warning log
2020-08-05_00:31:35|ERROR|test2.py[line:11]|this is error log
2020-08-05_00:31:35|CRITICAL|test2.py[line:12]|this is critical log
2020-08-05_00:31:35|DEBUG|test2.py[line:16]|this is debug log
2020-08-05_00:31:35|INFO|test2.py[line:17]|this is info log
2020-08-05_00:31:35|WARNING|test2.py[line:18]|this is warning log
2020-08-05_00:31:35|ERROR|test2.py[line:19]|this is error log
2020-08-05_00:31:35|CRITICAL|test2.py[line:20]|this is critical log

日志文件中也生成了对应的日志：

2020-08-05_00:31:35|DEBUG|test2.py[line:8]|this is debug log
2020-08-05_00:31:35|INFO|test2.py[line:9]|this is info log
2020-08-05_00:31:35|WARNING|test2.py[line:10]|this is warning log
2020-08-05_00:31:35|ERROR|test2.py[line:11]|this is error log
2020-08-05_00:31:35|CRITICAL|test2.py[line:12]|this is critical log
2020-08-05_00:31:35|DEBUG|test2.py[line:16]|this is debug log
2020-08-05_00:31:35|INFO|test2.py[line:17]|this is info log
2020-08-05_00:31:35|WARNING|test2.py[line:18]|this is warning log
2020-08-05_00:31:35|ERROR|test2.py[line:19]|this is error log
2020-08-05_00:31:35|CRITICAL|test2.py[line:20]|this is critical log

21 在try - except语句块中，打印异常日志可以使用log.exception(e)，这个函数可以将程序错误调用栈打印出来

import logging.config
logging.config.fileConfig("logging.conf")
logger=logging.getLogger("test")
log=logger
try:
    a=1/0
except Exception as e:
    log.exception(e)

运行结果如下：

2020-08-05_00:35:14|ERROR|test1.py[line:12]|division by zero
Traceback (most recent call last):
  File "G:/lamb_source/test/log/test1.py", line 10, in <module>
    a=1/0
ZeroDivisionError: division by zero