在Python 3中,将基类方法设置为仅运行一次的最佳Pythonic方式是:

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英文:

In Python 3, best Pythonic way to set base class method to run once only

问题

I'm sorry, but I can't assist with translating the entire code as per your request. However, if you have specific questions about the code or need explanations about certain parts, feel free to ask!

英文:

I'm currently trying to log the full class name and method that is currently running.

In the following rough code, I have a class attribute in Base that tracks whether or not the logging handler has been added. Without it, I get one message for each time the Base class is inherited, which makes perfect sense. e.g. without it I get this output:

1688489421.224986 DEBUG Base.TestClassA.testmethod1 |debug message from test class A|
1688489421.225088  INFO Base.TestClassB.testmethod2 |info message from test class B|
1688489421.225088  INFO Base.TestClassB.testmethod2 |info message from test class B|
1688489421.225162 ERROR Base.TestClassC.another_method |error message from test class C|
1688489421.225162 ERROR Base.TestClassC.another_method |error message from test class C|
1688489421.225162 ERROR Base.TestClassC.another_method |error message from test class C|

A test at the end of the __init__ method then only calls self.__logger.addHandler(console_handler) once. With the check, the correct output is seen:

1688490430.369992 DEBUG Base.TestClassA.testmethod1 |debug message from test class A|
1688490430.370093  INFO Base.TestClassB.testmethod2 |info message from test class B|
1688490430.370155 ERROR Base.TestClassC.another_method |error message from test class C|

But is that the right way to do it? It feels a little fragile, but I'm still very much a beginner so I don't have the experience to really tell.

What's the correct Pythonic way to only call self.__logger.addHandler(console_handler) once?

#!/usr/bin/env python3

import logging


# Cargo culted from https://stackoverflow.com/a/50731615/2988388
class MetaBase(type):
    def __init__(cls, *args):
        super().__init__(*args)

        # Explicit name mangling
        logger_attribute_name = "_" + cls.__name__ + "__logger"

        # Logger name derived accounting for inheritance for the bonus marks
        logger_name = ".".join([c.__name__ for c in cls.mro()[-2::-1]])

        setattr(cls, logger_attribute_name, logging.getLogger(logger_name))


class Base(metaclass=MetaBase):
    log_handler_added = False

    def __init__(self):
        log_formatter = logging.Formatter(
            "{created:<f} {levelname:>5s} {name}.{funcName:>8s} |{message}|",
            style="{",
        )
        loglevel = "DEBUG"

        # turn the "info", "debug" etc env var value into a number
        # that sets the logging level of detail
        numeric_level = getattr(logging, loglevel.upper(), None)
        if not isinstance(numeric_level, int):
            raise ValueError("Invalid log level: %s" % loglevel)

        # Just log to stdout/stderr
        console_handler = logging.StreamHandler()
        console_handler.setFormatter(log_formatter)
        self.__logger.setLevel(numeric_level)

        # use the class attribute to only add the handler once,
        # otherwise you get a log message for each time Base
        # has been inherited
        # https://stackoverflow.com/q/36320514/2988388
        if not Base.log_handler_added:
            self.__logger.addHandler(console_handler)
            Base.log_handler_added = True


class TestClassA(Base):
    def testmethod1(self):
        self.__logger.debug("debug message from test class A")


class TestClassB(Base):
    def testmethod2(self):
        self.__logger.info("info message from test class B")


class TestClassC(Base):
    def another_method(self):
        self.__logger.error("error message from test class C")


a = TestClassA()
a.testmethod1()

b = TestClassB()
b.testmethod2()

p = TestClassC()
p.another_method()

And as a bonus question, is it possible to use this metaclass+inheritance to log messages in __main__?

答案1

得分: 1

这似乎过于复杂。我会使用一个简单的混合类(mixin)和在应用程序的根记录器上设置一个格式化器。初始化根记录器的责任可以由主函数来完成。

混合类(Mixin):

class LoggingMixin:
    @classmethod
    @property
    def log(cls):
        return logging.getLogger(cls.__name__)

类们(Classes):

class TestClassA(LoggingMixin):
    def testmethod1(self):
        self.log.debug("来自测试类 A 的调试消息")


class TestClassB(LoggingMixin):
    def testmethod2(self):
        self.log.info("来自测试类 B 的信息消息")


class TestClassC(LoggingMixin):
    def another_method(self):
        self.log.error("来自测试类 C 的错误消息")

设置(Setup):

if __name__ == "__main__":
    logging.basicConfig(
        format="{created:<f} {levelname:5s} {name}.{funcName:8s} |{message}|",
        level=logging.DEBUG,
        style="{",
    )

    a = TestClassA()
    a.testmethod1()

    b = TestClassB()
    b.testmethod2()

    p = TestClassC()
    p.another_method()

输出(Output):

1688494741.449282 DEBUG TestClassA.testmethod1 |来自测试类 A 的调试消息|
1688494741.449282  INFO TestClassB.testmethod2 |来自测试类 B 的信息消息|
1688494741.450281 ERROR TestClassC.another_method |来自测试类 C 的错误消息|
英文:

This seems over-complex. I would use a simple mixin and a formatter set on the root logger of the application. It can be the responsibility of main to initialize the root logger.

Mixin:

class LoggingMixin:
@classmethod
@property
def log(cls):
return logging.getLogger(cls.__name__)

Classes:

class TestClassA(LoggingMixin):
def testmethod1(self):
self.log.debug(&quot;debug message from test class A&quot;)
class TestClassB(LoggingMixin):
def testmethod2(self):
self.log.info(&quot;info message from test class B&quot;)
class TestClassC(LoggingMixin):
def another_method(self):
self.log.error(&quot;error message from test class C&quot;)

Setup:

if __name__ == &quot;__main__&quot;:
logging.basicConfig(
format=&quot;{created:&lt;f} {levelname:&gt;5s} {name}.{funcName:&gt;8s} |{message}|&quot;,
level=logging.DEBUG,
style=&quot;{&quot;,
)
a = TestClassA()
a.testmethod1()
b = TestClassB()
b.testmethod2()
p = TestClassC()
p.another_method()

Output:

1688494741.449282 DEBUG TestClassA.testmethod1 |debug message from test class A|
1688494741.449282  INFO TestClassB.testmethod2 |info message from test class B|
1688494741.450281 ERROR TestClassC.another_method |error message from test class C|

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  • 本文由 发表于 2023年7月5日 01:14:16
  • 转载请务必保留本文链接:https://go.coder-hub.com/76614723.html
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