在python中使用LogRecordFactory添加自定义字段进行日志记录

Question

我正在尝试使用在我的日志记录中添加自定义字段LogRecordFactory。我重复调用一个类，每次这样做时，我都想在 init 模块中设置 custom_attribute，以便类中的其余代码将具有此属性。但我无法让它发挥作用。我发现以下内容有效，但它是静态的。

import logging

old_factory = logging.getLogRecordFactory()

def record_factory(*args, **kwargs):
    record = old_factory(*args, **kwargs)
    record.custom_attribute = "whatever"
    return record



logging.basicConfig(format="%(custom_attribute)s - %(message)s")
logging.setLogRecordFactory(record_factory)
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
logging.debug("test")

这将正确输出：

whatever - test

但是，我的用例是 custom_attribute 会有所不同。每次我调用一个特定的函数时，我都想改变它。因此，record_factory 似乎需要传递另一个参数，以便它可以使用新参数返回正确的记录。但我无法弄清楚。我尝试向该函数添加参数，但是当我进行调用时，我得到：

TypeError: __init__() missing 7 required positional arguments: 'name', 'level', 'pathname', 'lineno', 'msg', 'args', and 'exc_info'

*args我认为这与and**kwargs但我真的不知道有关。record_factory另外，为什么调用 by后没有括号logging.setLogRecordFactory？我从来没有见过一个函数像这样工作。

Answer 1

您可以尝试使用闭包：

import logging

old_factory = logging.getLogRecordFactory()

def record_factory_factory(context_id):
    def record_factory(*args, **kwargs):
        record = old_factory(*args, **kwargs)
        record.custom_attribute = context_id
        return record
    return record_factory


logging.basicConfig(format="%(custom_attribute)s - %(message)s")
logging.setLogRecordFactory(record_factory_factory("whatever"))
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
logging.debug("test")

logging.setLogRecordFactory(record_factory_factory("whatever2"))
logger = logging.getLogger()
logger.setLevel(logging.DEBUG)
logging.debug("test")

结果：

$ python3 log_test.py                                                          
whatever - test
whatever2 - test

Answer 2

当我尝试做类似的事情时，我偶然发现了这个问题。这就是我解决这个问题的方法，假设您想将名为 xyz 的内容添加到每个日志行（下面有进一步的解释）：

import logging
import threading
 

thread_local = threading.local()
 

def add_xyz_to_logrecords(xyz):
    factory = logging.getLogRecordFactory()
    if isinstance(factory, XYZLogFactory):
        factory.set_xyz(xyz)
    else:
        logging.setLogRecordFactory(XYZLogFactory(factory, xyz))
 

class XYZLogFactory():
    def __init__(self, original_factory, xyz):
        self.original_factory = original_factory
        thread_local.xyz = xyz

    def __call__(self, *args, **kwargs):
        record = self.original_factory(*args, **kwargs)
        try:
            record.xyz = thread_local.xyz
        except AttributeError:
            pass
        return record

   def set_xyz(self, xyz):
        thread_local.xyz = xyz

Here I've created a callable class XYZLogFactory, that remembers what the current value of xyz is, and also remembers what the original LogRecordFactory was. When called as a function, it creates a record using the original LogRecordFactory, and adds an xyz attribute with the current value. The thread_local is to make it thread-safe, but for an easier version, you could just use an attribute on the XYZLogFactory:

class XYZLogFactory():
    def __init__(self, original_factory, xyz):
        self.original_factory = original_factory
        self.xyz = xyz

    def __call__(self, *args, **kwargs):
        record = self.original_factory(*args, **kwargs)
        record.xyz = self.xyz
        return record

   def set_xyz(self, xyz):
        self.xyz = xyz

In my very first attempt (not shown here), I did not store the original factory, but stored it implicitly in the new LogRecordFactury using a closure. However, after a while that led to a RecursionError, because it kept calling the previous factory, which called the previous factory, etc.

Regarding your last question: there are no parentheses because the function is not called here. Instead it's passed to the logging.setLogRecordFactory, which saves it in a variable somewhere, and then calls that someplace else. If you want more information you can google something like 'functions as first class citizens'. Easy example:

x = str  # Assign to x the function that gives string representation of object
x(1)  # outputs the string representation of 1, same as if you'd called str(1)
> '1'