Question

我对Python的日志记录模块的输出感到惊讶。我写了Python.org的How-To for Logging。当我运行示例代码时，会有很多（令人困惑的）重复。

StreamHandler复制日志消息，每次我使用魔法%run

在iPython中重新加载文件时

In [4]: %run main.py
2018-05-11 2127:33 - WARNING - 3. This is a warning, yous!
2018-05-11 2127:33 - ERROR - 4. Here is an error
2018-05-11 2127:33 - CRITICAL - 5. This is f-ing critical!
[...]
In [7]: %run main.py
2018-05-11 2127:38 - WARNING - 3. This is a warning, yous!
2018-05-11 2127:38 - WARNING - 3. This is a warning, yous!
2018-05-11 2127:38 - WARNING - 3. This is a warning, yous!
2018-05-11 2127:38 - ERROR - 4. Here is an error
2018-05-11 2127:38 - ERROR - 4. Here is an error
2018-05-11 2127:38 - ERROR - 4. Here is an error
2018-05-11 2127:38 - CRITICAL - 5. This is f-ing critical!
2018-05-11 2127:38 - CRITICAL - 5. This is f-ing critical!
2018-05-11 2127:38 - CRITICAL - 5. This is f-ing critical!

我添加了一个FileHandler：

fh = logging.FileHandler("app.log")
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)
logger.addHandler(fh)

这也重复：

xtian@spaceghost> cat app.log
2018-05-11 2159:24 - WARNING - 3. This is a warning!
2018-05-11 2159:24 - ERROR - 4. This is an error
2018-05-11 2159:24 - CRITICAL - 5. This is fucking critical!
[...]
2018-05-11 2201:00 - WARNING - 3. This is a warning, yous!
2018-05-11 2201:00 - WARNING - 3. This is a warning, yous!
2018-05-11 2201:00 - WARNING - 3. This is a warning, yous!
2018-05-11 2201:00 - ERROR - 4. Here is an error.
2018-05-11 2201:00 - ERROR - 4. Here is an error.
2018-05-11 2201:00 - ERROR - 4. Here is an error.
2018-05-11 2201:00 - CRITICAL - 5. This is f-ing critical!
2018-05-11 2201:00 - CRITICAL - 5. This is f-ing critical!
2018-05-11 2201:00 - CRITICAL - 5. This is f-ing critical!

我也遵循other posts的建议，并在消息调用之前添加了这些行：

# propagation fix
logger.propagate = False

结果是一样的。

设置发布，我看到一个类似的问题：

What could cause the logging module to log a record multiple times?

但所有这些调试都是针对OP的原始自定义代码。我的问题是示例代码，我希望它可以警告或更好地解释发生了什么。

文档说，

请注意。如果您将处理程序附加到记录器及其一个或多个祖先，它可能会多次发出相同的记录。一般来说，你不应该需要将处理程序附加到多个记录器 - 如果您只是附加它到记录器层次结构中最高的适当记录器，然后它会看到提供的所有后代记录器记录的所有事件他们的传播设置被设置为True。常见的情况是将处理程序仅附加到根记录器，并允许传播照顾好其余的事。

您可以看到完整的测试文件main.py here，看看我是否有'多个记录器'。

import logging

# Root Logger
logger = logging.getLogger(__name__)

# Console handler
ch = logging.StreamHandler()
ch.setLevel(logging.WARNING)

# Formatter
formatter = logging.Formatter(fmt='%(asctime)s - %(levelname)s - %(message)s' , datefmt='%Y-%m-%d %H%M:%S', style='%')

# Add formatter to Console handler ch
ch.setFormatter(formatter)

# Add ch to logger
logger.addHandler(ch)

# Text File handler
fh = logging.FileHandler("app.log")
fh.setLevel(logging.DEBUG)
fh.setFormatter(formatter)
logger.addHandler(fh)

# propagation fix
logger.propagate = False

# Example Application code
logger.debug("1. This is a debug message.")
logger.info("2. This is an info message.")
logger.warning('3. This is a warning!')
logger.error('4. This is an error')
logger.critical("5. This is fucking critical!")

Answer 1

logger返回的logging.getLogger(__name__)每次执行%run main.py时都是相同的记录器。但是

ch = logging.StreamHandler()

每次

实例化一个新的StreamHandler，然后将其添加到logger：

logger.addHandler(ch)

因此，在%run main.py的后续运行中，logger有多个处理程序附加到它并且每个处理程序发出一条记录。

In [5]: %run main.py
2018-05-11 2251:17 - WARNING - 3. This is a warning!
2018-05-11 2251:17 - ERROR - 4. This is an error
2018-05-11 2251:17 - CRITICAL - 5. This is fucking critical!

In [6]: logger
Out[6]: <logging.Logger at 0x7f5d0152fe10>

第一次运行%run main.py时，两个处理程序附加到logger：

In [7]: logger.handlers
Out[12]: 
[<logging.StreamHandler at 0x7f5d0152fdd8>,
 <logging.FileHandler at 0x7f5d014c40f0>]

In [13]: %run main.py
2018-05-11 2251:44 - WARNING - 3. This is a warning!
2018-05-11 2251:44 - WARNING - 3. This is a warning!
2018-05-11 2251:44 - ERROR - 4. This is an error
2018-05-11 2251:44 - ERROR - 4. This is an error
2018-05-11 2251:44 - CRITICAL - 5. This is fucking critical!
2018-05-11 2251:44 - CRITICAL - 5. This is fucking critical!

第二次，现在有四个处理程序：

In [14]: logger.handlers
Out[14]: 
[<logging.StreamHandler at 0x7f5d0152fdd8>,
 <logging.FileHandler at 0x7f5d014c40f0>,
 <logging.StreamHandler at 0x7f5d014c4668>,
 <logging.FileHandler at 0x7f5d014c4550>]

In [15]: logger
Out[15]: <logging.Logger at 0x7f5d0152fe10>

为防止重复，您可以在logger.removeHandler来电之间致电%run：

In [29]: for handler in logger.handlers: logger.removeHandler(handler)

In [30]: %run main.py
2018-05-11 2257:30 - WARNING - 3. This is a warning!
2018-05-11 2257:30 - ERROR - 4. This is an error
2018-05-11 2257:30 - CRITICAL - 5. This is fucking critical!

或修改main.py，以便每次调用%run时都不会附加新的处理程序。例如，您可以使用logging.config.dictConfig设置logger：

import logging
import logging.config

# Modified using https://stackoverflow.com/a/7507842/190597 as a template
logging_config = { 
    'version': 1,
    'formatters': { 
        'standard': { 
            'format': '%(asctime)s - %(levelname)s - %(message)s'
        },
    },
    'handlers': { 
        'stream': { 
            'level': 'INFO',
            'formatter': 'standard',
            'class': 'logging.StreamHandler',
        },
        'file': { 
            'level': 'DEBUG',
            'formatter': 'standard',
            'class': 'logging.FileHandler',
            'filename': 'app.log'
        },
    },
    'loggers': { 
        __name__: { 
            'handlers': ['stream', 'file'],
            'level': 'WARN',
            'propagate': False
        },
    } 
}
logging.config.dictConfig(logging_config)
logger = logging.getLogger(__name__)

# Example Application code
logger.debug("1. This is a debug message.")
logger.info("2. This is an info message.")
logger.warning('3. This is a warning!')
logger.error('4. This is an error')
logger.critical("5. This is fucking critical!")

使用此代码，%run main.py每次都会发出相同的输出。

记录模块示例代码每次调用重复消息n次

1 个答案: