logging将日志写入文件filehandler

import logging
logger = logging.getLogger()
logger.setLevel(level = logging.INFO) #可以不设，默认是WARNING级别
handler = logging.FileHandler("log.txt")
handler.setLevel(logging.INFO)#可以不设，默认是WARNING级别

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s') 
handler.setFormatter(formatter) #设置文件的log格式
logger.addHandler(handler) 

logger.info("Start print log")
logger.debug("Do something")
logger.warning("Something maybe fail.")
logger.info("Finish")

利用FileHandler将log写入文件，比basicConfig的好处是想写到哪个文件就写到哪个，basicConfig是一旦设置就不能更改

注：个人理解：handler是控制log文件的，logger是控制程序文件的，logger.addHandler(handler)确定程序的log要写到哪个文件

 注：

logger.setLevel(level = logging.INFO)和

handler.setLevel(logging.INFO)

 都会生效，最后写入的是满足两个要求的数据

注意一点，FileHandler里面默认写log文件中中文的编码方式是GBK，而Python读取文件方式是utf-8,所以如果用默认的编码方式的话，pycharm读取log文件后会乱码

解决方式是，进到FileHandler中，把初始化函数改成如下

class FileHandler(StreamHandler):
    """
    A handler class which writes formatted logging records to disk files.
    """
    def __init__(self, filename, mode='a', encoding='utf-8', delay=False):

 多个log文件的例子

下面程序是将一个程序内的不同log写到两个文件

import logging
logger=logging.getLogger()
logger.setLevel(level=logging.INFO)
filehandle01=logging.FileHandler("log01.txt")
filehandle02=logging.FileHandler("log02.txt")

filehandle02.setLevel(logging.ERROR)
formatter01=logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
formatter02=logging.Formatter('%(asctime)s - %(filename)s - %(levelname)s - %(lineno)s-%(message)s')

filehandle01.setFormatter(formatter01)
filehandle02.setFormatter(formatter02)

logger.addHandler(filehandle01)
logger.addHandler(filehandle02)

logger.info("Start print log")
logger.debug("Do something")
logger.warning("Something maybe fail")
logger.info("Finish")
logger.error("error print log")

log01文件内容

2020-03-25 15:52:41,006 - root - INFO - Start print log
2020-03-25 15:52:41,006 - root - WARNING - Something maybe fail
2020-03-25 15:52:41,006 - root - INFO - Finish
2020-03-25 15:52:41,006 - root - ERROR - error print log

log02文件内容

2020-03-25 15:52:41,006 - trylog.py - ERROR - 22-error print log

 下面是将两个程序文件的log写到一个log文件

程序文件1

import logging
file1logger=logging.getLogger()
file1logger.setLevel(level=logging.INFO)
handler=logging.FileHandler("log.txt")
handler.setLevel(logging.INFO)
formatter=logging.Formatter('time:%(asctime)s  - %(levelname)s-line:%(lineno)s - %(message)s')
handler.setFormatter(formatter)
file1logger.addHandler(handler)


print("this is file1's log")
file1logger.warning("this is file1's log")

程序文件2

import logging
file1logger=logging.getLogger()
file1logger.setLevel(level=logging.INFO)
handler=logging.FileHandler("log.txt")
handler.setLevel(logging.INFO)
formatter=logging.Formatter('time:%(asctime)s  - %(levelname)s-line:%(lineno)s - %(message)s')
handler.setFormatter(formatter)
file1logger.addHandler(handler)


print("this is file2's log")
file1logger.warning("this is file2's log")

以上两个文件分别执行一次

log文件：

time:2020-07-21 17:10:00,718  - WARNING-line:12 - this is file1's log
time:2020-07-21 17:10:04,150  - WARNING-line:12 - this is file2's log

注：

formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')这里引号里的格式是随便的，最后程序会用Formatter参数格式化替换
里面的格式化标准
栗子：

formatter = logging.Formatter('time：%(asctime)s - %(name)s - lineno：%(lineno)s - %(message)s')

Formatter参数的官方文档

 https://docs.python.org/3.7/library/logging.html#logrecord-attributes

Attribute name	Format	Description
args	You shouldn’t need to format this yourself.	The tuple of arguments merged into msg to produce message, or a dict whose values are used for the merge (when there is only one argument, and it is a dictionary).
asctime	%(asctime)s	Human-readable time when the LogRecord was created. By default this is of the form ‘2003-07-08 16:49:45,896’ (the numbers after the comma are millisecond portion of the time).
created	%(created)f	Time when the LogRecord was created (as returned by time.time()).
exc_info	You shouldn’t need to format this yourself.	Exception tuple (à la sys.exc_info) or, if no exception has occurred, None.
filename	%(filename)s	Filename portion of pathname.
funcName	%(funcName)s	Name of function containing the logging call.
levelname	%(levelname)s	Text logging level for the message ('DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL').
levelno	%(levelno)s	Numeric logging level for the message (DEBUG, INFO, WARNING, ERROR, CRITICAL).
lineno	%(lineno)d	Source line number where the logging call was issued (if available).
message	%(message)s	The logged message, computed as msg % args. This is set when Formatter.format() is invoked.
module	%(module)s	Module (name portion of filename).
msecs	%(msecs)d	Millisecond portion of the time when the LogRecord was created.
msg	You shouldn’t need to format this yourself.	The format string passed in the original logging call. Merged with args to produce message, or an arbitrary object (see Using arbitrary objects as messages).
name	%(name)s	Name of the logger used to log the call.
pathname	%(pathname)s	Full pathname of the source file where the logging call was issued (if available).
process	%(process)d	Process ID (if available).
processName	%(processName)s	Process name (if available).
relativeCreated	%(relativeCreated)d	Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded.
stack_info	You shouldn’t need to format this yourself.	Stack frame information (where available) from the bottom of the stack in the current thread, up to and including the stack frame of the logging call which resulted in the creation of this record.
thread	%(thread)d	Thread ID (if available).
threadName	%(threadName)s	Thread name (if available).