Python日志模块logging的新手入门教程

print("用户登录成功")
print("数据库连接失败")
print("订单处理完成")

import logging

# 推荐用 __name__ 作为名称，自动形成层级结构
logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)  # 设置最低日志级别

import logging

logging.basicConfig(
    level=logging.DEBUG,
    format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
    datefmt="%Y-%m-%d %H:%M:%S",
    filename="app.log",       # 输出到文件
    filemode="a",             # 追加模式
    encoding="utf-8"          # 避免中文乱码
)

logger = logging.getLogger(__name__)
logger.info("服务启动成功")

import logging

def setup_logger():
    # 1. 创建 Logger
    logger = logging.getLogger(__name__)
    logger.setLevel(logging.DEBUG)
    logger.propagate = False  # 禁止向上传播，避免重复输出

    # 2. 创建控制台 Handler
    console_handler = logging.StreamHandler()
    console_handler.setLevel(logging.INFO)  # 控制台只输出 INFO 及以上

    # 3. 创建文件 Handler
    file_handler = logging.FileHandler("app.log", encoding="utf-8")
    file_handler.setLevel(logging.DEBUG)  # 文件记录所有级别

    # 4. 创建 Formatter
    formatter = logging.Formatter(
        "%(asctime)s | %(levelname)-8s | %(name)s | %(filename)s:%(lineno)d | %(message)s",
        datefmt="%Y-%m-%d %H:%M:%S"
    )

    # 5. 绑定 Formatter 到 Handler
    console_handler.setFormatter(formatter)
    file_handler.setFormatter(formatter)

    # 6. 绑定 Handler 到 Logger
    logger.addHandler(console_handler)
    logger.addHandler(file_handler)

    return logger

# 使用
logger = setup_logger()
logger.debug("调试信息")
logger.info("正常信息")
logger.error("错误信息", exc_info=True)  # 记录完整异常堆栈

import logging.config

config = {
    "version": 1,
    "disable_existing_loggers": False,
    "formatters": {
        "standard": {
            "format": "%(asctime)s - %(name)s - %(levelname)s - %(message)s"
        }
    },
    "handlers": {
        "console": {
            "class": "logging.StreamHandler",
            "level": "DEBUG",
            "formatter": "standard",
            "stream": "ext://sys.stdout"
        },
        "file": {
            "class": "logging.FileHandler",
            "level": "INFO",
            "formatter": "standard",
            "filename": "app.log",
            "encoding": "utf8"
        }
    },
    "loggers": {
        "my_app": {
            "level": "DEBUG",
            "handlers": ["console", "file"],
            "propagate": False
        }
    }
}

logging.config.dictConfig(config)
logger = logging.getLogger("my_app")

#  推荐：延迟格式化，性能更好
logger.info("用户 %s 登录成功，ID: %d", username, user_id)

#  不推荐：f-string 会无条件计算
logger.info(f"用户 {username} 登录成功，ID: {user_id}")

from logging.handlers import RotatingFileHandler

handler = RotatingFileHandler(
    "app.log",
    maxBytes=10 * 1024 * 1024,  # 单个文件最大 10MB
    backupCount=5,               # 保留最近 5 个历史文件
    encoding="utf-8"
)

from logging.handlers import TimedRotatingFileHandler

handler = TimedRotatingFileHandler(
    "app.log",
    when="D",       # 轮转单位：S(秒)、M(分)、H(时)、D(天)、midnight(午夜)
    interval=1,     # 间隔时间
    backupCount=7,  # 保留最近 7 天日志
    encoding="utf-8"
)

import logging
import logging.handlers
import json
from pathlib import Path


class JsonFormatter(logging.Formatter):
    """JSON 格式化器，便于 ELK/Loki 采集分析"""
    def format(self, record):
        log_data = {
            "time": self.formatTime(record),
            "level": record.levelname,
            "logger": record.name,
            "message": record.getMessage(),
            "module": record.module,
            "line": record.lineno,
        }
        if record.exc_info:
            log_data["exception"] = self.formatException(record.exc_info)
        return json.dumps(log_data, ensure_ascii=False)


def setup_production_logging(log_dir="logs"):
    """配置生产级日志体系"""
    log_path = Path(log_dir)
    log_path.mkdir(exist_ok=True)

    root_logger = logging.getLogger()
    root_logger.setLevel(logging.DEBUG)

    # 统一格式
    fmt = logging.Formatter(
        "%(asctime)s | %(levelname)-8s | %(name)s | %(message)s",
        datefmt="%Y-%m-%d %H:%M:%S"
    )

    # 控制台 Handler：只输出 WARNING 及以上
    console = logging.StreamHandler()
    console.setLevel(logging.WARNING)
    console.setFormatter(fmt)

    # 文件 Handler：输出所有级别，按大小轮转
    file_handler = logging.handlers.RotatingFileHandler(
        log_path / "app.log",
        maxBytes=10 * 1024 * 1024,  # 10MB 轮转
        backupCount=5,
        encoding="utf-8",
    )
    file_handler.setLevel(logging.DEBUG)
    file_handler.setFormatter(fmt)

    # 错误专用 Handler
    error_handler = logging.handlers.RotatingFileHandler(
        log_path / "error.log",
        maxBytes=5 * 1024 * 1024,
        backupCount=3,
        encoding="utf-8",
    )
    error_handler.setLevel(logging.ERROR)
    error_handler.setFormatter(fmt)

    root_logger.addHandler(console)
    root_logger.addHandler(file_handler)
    root_logger.addHandler(error_handler)


# 使用
setup_production_logging()
logger = logging.getLogger(__name__)

logger.info("应用启动")
logger.error("请求失败", exc_info=True)