子类化logging.Formatter更改logging.Formatter的默认行为

Question

我向记录器添加了两个具有不同格式化程序的处理程序。第一个需要子类化logging.Formatter来进行自定义格式化。默认格式化程序足以满足第二个处理程序的需要。

假设第一个格式化程序只是从消息中删除换行符。以下脚本说明了看似奇怪的行为：

import logging

logger = logging.getLogger(__name__)

class CustomFormatter(logging.Formatter):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
    def format(self, record):
        record.msg = record.msg.strip().replace('\n', ' ')
        return super().format(record)

h1 = logging.StreamHandler()
formatter1 = CustomFormatter(fmt=None, datefmt=None)
h1.setFormatter(formatter1)
logger.addHandler(h1)

h2 = logging.StreamHandler()
formatter2 = logging.Formatter(fmt=None, datefmt=None)
h2.setFormatter(formatter2)
logger.addHandler(h2)

logger.warning('string with\nmultiple lines')

输出如下：

string with multiple lines
string with multiple lines

我期望的是这个：

string with multiple lines
string with 
multiple lines

第二个格式化程序不应实现 的行为CustomFormatter，但它确实实现了。当我反转处理程序添加到记录器的顺序时，这种情况不会发生。

除非我误解了子类化，否则不应通过重写子类中的方法来更改基类的行为。当我重写除 之外的类的方法时，这似乎不是问题logging.Formatter。

这是日志记录模块中的错误，还是我在这里遗漏了一些东西？

Answer 1

This line was your down fall:

record.msg = record.msg.strip().replace('\n', ' ')

You reassigned the scrubbed string to the record which is used by all remaining handlers/formatters attached to the logger. Copy the record and it works:

import logging
from copy import copy

logger = logging.getLogger(__name__)

class CustomFormatter(logging.Formatter):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
    def format(self, record):
        record = copy(record)
        record.msg = record.msg.strip().replace('\n', ' ')
        return super().format(record)

h1 = logging.StreamHandler()
formatter1 = CustomFormatter(fmt=None, datefmt=None)
h1.setFormatter(formatter1)
logger.addHandler(h1)

h2 = logging.StreamHandler()
formatter2 = logging.Formatter(fmt=None, datefmt=None)
h2.setFormatter(formatter2)
logger.addHandler(h2)

logger.warning('string with\nmultiple lines')

Outputs

string with multiple lines
string with
multiple lines