如何编写自定义 python 日志记录处理程序？

Question

如何编写自定义控制台日志函数以仅在控制台窗口上输出单行（不追加）日志消息，直到第一个常规日志记录。

progress = ProgressConsoleHandler()
console  = logging.StreamHandler()  

logger = logging.getLogger('test')
logger.setLevel(logging.DEBUG) 
logger.addHandler(console)  
logger.addHandler(progress)

logger.info('test1')
for i in range(3):
    logger.progress('remaining %d seconds' % i)
    time.sleep(1)   
logger.info('test2')

这样控制台输出只有三行：

INFO: test1
remaining 0 seconds... 
INFO: test2

关于如何实现这一点的最佳方式的任何建议？

Answer 1

import logging
class ProgressConsoleHandler(logging.StreamHandler):
    """
    A handler class which allows the cursor to stay on
    one line for selected messages
    """
    on_same_line = False
    def emit(self, record):
        try:
            msg = self.format(record)
            stream = self.stream
            same_line = hasattr(record, 'same_line')
            if self.on_same_line and not same_line:
                stream.write(self.terminator)
            stream.write(msg)
            if same_line:
                stream.write('... ')
                self.on_same_line = True
            else:
                stream.write(self.terminator)
                self.on_same_line = False
            self.flush()
        except (KeyboardInterrupt, SystemExit):
            raise
        except:
            self.handleError(record)
if __name__ == '__main__':
    import time
    progress = ProgressConsoleHandler()
    console  = logging.StreamHandler()  

    logger = logging.getLogger('test')
    logger.setLevel(logging.DEBUG) 
    logger.addHandler(progress)

    logger.info('test1')
    for i in range(3):
        logger.info('remaining %d seconds', i, extra={'same_line':True})
        time.sleep(1)   
    logger.info('test2')

请注意，只注册了一个处理程序，extra 关键字参数让处理程序知道它应该保留在一行上。 emit() 方法中有更多的逻辑来处理应该保持在一行的消息和需要有自己的行的消息之间的变化。