Python 学习日知录（二）- 日志

一直在用python进行FPGA网络调试，也就是通过udp包读写FPGA的一些内部寄存器和外设什么的。最近想对这个简单脚本进行改造，打造一个更称手的工具。

暂时想法如下：
1. 记录调试过程（logging）；
2. 录制脚本，载入运行脚本（保存成json格式）；
3. 打开时恢复上一次的运行环境；
4. 命令行就可以了；

python 2.7内置的logging模块，记录调试过程基本够用。这两天就学习了这个模块的基本用法，总结如下：

1. 基本用法

既然是日志，时间戳必不可少。因此直接上带时间戳的代码：

# -*- coding:utf8 -*-import loggingimport logging.handlersdef ini_logging(log_file_name):    '''    初始化logging系统    :param log_file_name: 日志文件    :return:    '''    logger = logging.getLogger()    logger.setLevel(logging.DEBUG)    rh = logging.handlers.TimedRotatingFileHandler(log_file_name, 'D')    fm = logging.Formatter("%(asctime)s  %(levelname)s - %(message)s", "%Y-%m-%d %H:%M:%S")    rh.setFormatter(fm)    logger.addHandler(rh)def write_reg(addr, value):  # 写寄存器    logging.info('write reg %02x : %02x' % (addr, value))def read_reg(addr, len):  # 读寄存器    ret = 128  # 假设的返回值，实际从网络获取    logging.info('read reg %02x : %02x' % (addr, ret))if __name__ == '__main__':    ini_logging('testlog.log')    logging.info('Start')    write_reg(100, 16)    read_reg(100,1)    logging.info('End')

运行该脚本，获得的日志文件如下：

2017-06-20 23:44:33  INFO - Start2017-06-20 23:44:33  INFO - write reg 64 : 102017-06-20 23:44:33  INFO - read reg 64 addr : 802017-06-20 23:44:33  INFO - End

2. 一些有用的东西

2.1 日志等级

日志一共分成5个等级，从低到高分别是：
DEBUG
INFO
WARNING
ERROR
CRITICAL

分别对应五种方法：

    class Logger:        def debug(self, msg, *args, **kwargs): ...        def info(self, msg, *args, **kwargs): ...        def warn(self, msg, *args, **kwargs): ...        def error(self, msg, *args, **kwargs): ...        def critical(self, msg, *args, **kwargs): ...

在logger.setLevel(logging.DEBUG)中，可以指定打印的最低级别。

2.2 打印格式

在fm = logging.Formatter()中设置。格式如下：

"%(asctime)s  %(levelname)s - %(message)s", "%Y-%m-%d %H:%M:%S"

预定义的内容如下：

name comment %(name)s Name of the logger (logging channel) %(levelno)s Numeric logging level for the message (DEBUG,INFO, WARN, ERROR, CRITICAL) %(levelname)s Text logging level for the message (“DEBUG”, “INFO”,”WARN”, “ERROR”, “CRITICAL”) %(pathname)s Full pathname of the source file where the logging call was issued (if available) %(filename)s Filename portion of pathname %(module)s Module from which logging call was made %(lineno)d Source line number where the logging call was issued (if available) %(created)f Time when the LogRecord was created (time.time() return value) %(asctime)s Textual time when the LogRecord was created %(msecs)d Millisecond portion of the creation time %(relativeCreated)d Time in milliseconds when the LogRecord was created, relative to the time the logging module was loaded (typically at application startup time) %(thread)d Thread ID (if available) %(message)s The result of record.getMessage(), computed just as the record is emitted

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参考文献：
1. python 日志模块 logging 详解
2. 够用的 Python 写日志的知识——标准日志模块logging简介
3. PEP 282 – A Logging System