Python 3.6中如何通过getLogger实例简化日志级别设置？

问题原因 #

你遇到的报错是因为getLevelName是logging模块的顶层函数，并非Logger实例的方法，因此需要调用logging.getLevelName()而非logger.getLevelName()。

方法1：修复你的简化代码 #

直接使用模块级别的getLevelName函数，同时修正原代码中StreamHandler的判断逻辑（原逻辑存在误判）：

import logging
from sys import stdout
from logging import DEBUG, INFO, WARNING, ERROR, CRITICAL, StreamHandler

logger = logging.getLogger(__name__)
logging_level = "DEBUG"
valid_logging_levels = ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
if logging_level not in valid_logging_levels:
    raise ValueError(f"Logging level must be one of the following: {valid_logging_levels}")

# 正确检查并添加StreamHandler
sys_out = StreamHandler(stdout)
if not any(isinstance(handler, StreamHandler) for handler in logger.handlers):
    logger.addHandler(sys_out)

# 设置日志级别
log_level = logging.getLevelName(logging_level)
logger.setLevel(log_level)

原代码中if not [isinstance(handler, StreamHandler) for handler in logger.handlers]的逻辑错误：布尔值列表非空时会被视为True，导致not后误判是否已有StreamHandler。改用any()可准确判断。

方法2：字典映射实现直观匹配 #

这种方式可读性更强，也便于后续扩展自定义日志级别：

import logging
from sys import stdout
from logging import DEBUG, INFO, WARNING, ERROR, CRITICAL, StreamHandler

logger = logging.getLogger(__name__)
logging_level = "DEBUG"
valid_logging_levels = ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
if logging_level not in valid_logging_levels:
    raise ValueError(f"Logging level must be one of the following: {valid_logging_levels}")

# 定义级别映射字典
level_mapping = {
    "DEBUG": DEBUG,
    "INFO": INFO,
    "WARNING": WARNING,
    "ERROR": ERROR,
    "CRITICAL": CRITICAL
}

# 添加StreamHandler
sys_out = StreamHandler(stdout)
if not any(isinstance(handler, StreamHandler) for handler in logger.handlers):
    logger.addHandler(sys_out)

# 设置级别
logger.setLevel(level_mapping[logging_level])

由于已提前校验logging_level的合法性，直接通过字典取值不会触发KeyError。

方法3：使用内部API快速转换（Python3.2+兼容） #

logging._checkLevel可直接将字符串或数值转换为合法日志级别常量，内部自带校验：

import logging
from sys import stdout
from logging import DEBUG, INFO, WARNING, ERROR, CRITICAL, StreamHandler

logger = logging.getLogger(__name__)
logging_level = "DEBUG"
valid_logging_levels = ["DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL"]
if logging_level not in valid_logging_levels:
    raise ValueError(f"Logging level must be one of the following: {valid_logging_levels}")

sys_out = StreamHandler(stdout)
if not any(isinstance(handler, StreamHandler) for handler in logger.handlers):
    logger.addHandler(sys_out)

# 直接转换并设置级别
logger.setLevel(logging._checkLevel(logging_level))

注意：该函数以_开头，属于模块内部API，虽Python3.6可用，但追求API稳定性的话优先选择前两种方法。

内容的提问来源于stack exchange，提问作者Micah Pearce