为什么Python的logging模块自定义Filter无法输出给定级别的日志信息？

不是filter的问题，是你使用的问题

import logging

logging.getLogger().setLevel(logging.DEBUG)

logging.debug("This is a debug message with custom keyword")
logging.info("This is an info message with custom keyword")
logging.warning("This is a warning message with custom keyword")
logging.error("This is an error message with custom keyword")
logging.critical("This is a critical message with custom keyword")

DEBUG:root:This is a debug message with custom keyword
INFO:root:This is an info message with custom keyword
WARNING:root:This is a warning message with custom keyword
ERROR:root:This is an error message with custom keyword
CRITICAL:root:This is a critical message with custom keyword

原因

正确的使用方法是

import logging


class CustomFilter(logging.Filter):
    def filter(self, record):
        message = record.getMessage()
        return "custom" in message


logger: logging.Logger = logging.getLogger(__file__)
handler = logging.StreamHandler()  # handler才是关键
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)
customFilter = CustomFilter()
logger.addFilter(customFilter)

logger.debug("This is a debug message with custom keyword")
logger.info("This is an info message with custom keyword")
logger.warning("This is a warning message with custom keyword")
logger.error("This is an error message with custom keyword")
logger.critical("This is a critical message with custom keyword")