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flask 解决日志重复打印问题 or Python日志重复打印

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背景:业务代码上线后,莫名会重复输出很多相同的日志,已知以为是多线程问题,后仔细了解期logging原理后发现并非如此。

以下为解决方案

from flask import Flask as _Flask
from flask.helpers import locked_cached_property
from flask.logging import has_level_handler, default_handler



def create_MyLogger(app: "Flask") -> logging.Logger:
    """Get the Flask app's logger and configure it if needed.

    The logger name will be the same as
    :attr:`app.import_name <flask.Flask.name>`.

    When :attr:`~flask.Flask.debug` is enabled, set the logger level to
    :data:`logging.DEBUG` if it is not set.

    If there is no handler for the logger's effective level, add a
    :class:`~logging.StreamHandler` for
    :func:`~flask.logging.wsgi_errors_stream` with a basic format.
    """
    # logger = logging.getLogger(app.name)
    # 防止重复打印
    logger = logging.getLogger(uuid.uuid1().hex)

    if app.debug and not logger.level:
        logger.setLevel(logging.DEBUG)

    if not has_level_handler(logger) :
        logger.addHandler(default_handler)

    return logger



class Flask(_Flask):
    """
    将重新的方法进行注册
    """
  

    @locked_cached_property
    def logger(self) -> logging.Logger:
        """A standard Python :class:`~logging.Logger` for the app, with
        the same name as :attr:`name`.

        In debug mode, the logger's :attr:`~logging.Logger.level` will
        be set to :data:`~logging.DEBUG`.

        If there are no handlers configured, a default handler will be
        added. See :doc:`/logging` for more information.

        .. versionchanged:: 1.1.0
            The logger takes the same name as :attr:`name` rather than
            hard-coding ``"flask.app"``.

        .. versionchanged:: 1.0.0
            Behavior was simplified. The logger is always named
            ``"flask.app"``. The level is only set during configuration,
            it doesn't check ``app.debug`` each time. Only one format is
            used, not different ones depending on ``app.debug``. No
            handlers are removed, and a handler is only added if no
            handlers are already configured.

        .. versionadded:: 0.3
        """
        return create_MyLogger(self)

  重复打印的原因 参考 http://static.kancloud.cn/noahs/python/932418

问题起源:

​ 在学习了python的函数式编程后,又接触到了logging这样一个强大的日志模块。为了减少重复代码,应该不少同学和我一样便迫不及待的写了一个自己的日志函数,比如下面这样:

# 这里为了便于理解,简单的展示了一个输出到屏幕的日志函数
def my_log():
    logger = logging.getLogger('mysql.log')

    ch = logging.StreamHandler()
    ch.setLevel(logging.ERROR)
    fmt = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    ch.setFormatter(fmt)
    logger.addHandler(ch)
    return logger

my_log().error('run one')
my_log().error('run two')
my_log().error('run three')

函数写好了,看起来似乎也没有问题,我们来运行一下!
结果如下:

> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run one  
> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run two  
> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run two  
> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run three  
> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run three  
> 2018-06-21 13:06:37,569 - mysql.log - ERROR - run three

日志居然重复输出了,且数量递增。


问题解析

  • 实际上logger = logging.getLogger('mysql.log')在执行时,没有每次生成一个新的logger,而是先检查内存中是否存在一个叫做‘mysql.log’的logger对象,存在则取出,不存在则新建。

  • 实例化的logger对象具有‘handlers’这样一个属性来存储 Handler,代码演示如下:

    def my_log():
        logger = logging.getLogger('mysql.log')
        # 每次被调用后打印出logger的handlers列表
        print(logger.handlers)
    
        ch = logging.StreamHandler()
        ch.setLevel(logging.ERROR)
        fmt = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
        ch.setFormatter(fmt)    
        logger.addHandler(ch)    
        return logger    
    
    my_log().error('run one')
    my_log().error('run two')
    my_log().error('run three')    
    

    运行结果:

    > \[\]  
    > 2018-06-21 13:26:14,059 - mysql.log - ERROR - run one  
    > \[ (ERROR)>\]  
    > 2018-06-21 13:26:14,060 - mysql.log - ERROR - run two  
    > 2018-06-21 13:26:14,060 - mysql.log - ERROR - run two  
    > \[ (ERROR)>,  (ERROR)>\]  
    > 2018-06-21 13:26:14,060 - mysql.log - ERROR - run three  
    > 2018-06-21 13:26:14,060 - mysql.log - ERROR - run three  
    > 2018-06-21 13:26:14,060 - mysql.log - ERROR - run three
    
    1. logger.handlers最初是一个空列表,执行‘logger.addHandler(ch)’添加一个‘StreamHandler’,输出一条日志
    2. 在第二次被调用时,logger.handlers已经存在一个‘StreamHandler’,再次执行‘logger.addHandler(ch)’就会再次添加一个‘StreamHandler’,此时的logger有两个个‘StreamHandler’,输出两条重复的日志
    3. 在第三次被调用时,logger.handlers已经存在两个‘StreamHandler’,再次执行‘logger.addHandler(ch)’就会再次添加一个,此时的logger有三个‘StreamHandler’,输出三条重复的日志

解决办法

1.改名换姓

# 为日志函数添加一个name,每次调用时传入不同的日志名
def my_log(name):
    logger = logging.getLogger(name)

    ch = logging.StreamHandler()
    ch.setLevel(logging.ERROR)
    fmt = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    ch.setFormatter(fmt)
    logger.addHandler(ch)
    return logger

my_log('log1').error('run one')
my_log('log2').error('run two')
my_log('log3').error('run three')

运行结果:

> 2018-06-21 13:40:51,685 - log1 - ERROR - run one  
> 2018-06-21 13:40:51,685 - log2 - ERROR - run two  
> 2018-06-21 13:40:51,685 - log3 - ERROR - run three

2.及时清理(logger.handlers.clear)

def my_log():
    logger = logging.getLogger()
    # 每次被调用后,清空已经存在handler
    logger.handlers.clear()

    ch = logging.StreamHandler()
    ch.setLevel(logging.ERROR)
    fmt = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    ch.setFormatter(fmt)
    logger.addHandler(ch)
    return logger

my_log().error('run one')
my_log().error('run two')
my_log().error('run three')

3.用前判断

import logging
def my_log():
    logger = logging.getLogger('mysql.log')
    # 判断logger是否已经添加过handler,是则直接返回,否则才执行
    if not logger.handlers:
        ch = logging.StreamHandler()
        ch.setLevel(logging.ERROR)
        fmt = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
        ch.setFormatter(fmt)
        logger.addHandler(ch)
    return logger

my_log().error('run one')
my_log().error('run two')
my_log().error('run three')

综上,解决方法可以参照上诉三种在 create_MyLogger 函数中实现即可。

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