Logging with info level doesn't produce any output

Question

I ran the following using both the Python shell, and run it as a Python file from the command line. I don's see my log output at all.

import logging

formatter = logging.Formatter('%(asctime)s,%(msecs)d %(levelname)-8s [%(filename)s:%(lineno)d] %(message)s')

stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging.INFO)
stream_handler.setFormatter(formatter)

logger = logging.getLogger()
logger.addHandler(stream_handler)
logger.info(("info logging"))

Answer 1

Your logging output was almost correct with the exception of setLevel . The logging level needs to be defined on the logger instance instead of the handler instance. Your code therefore only needs a very small tweak to make it work:

import logging

formatter = logging.Formatter(
    '%(asctime)s,%(msecs)d %(levelname)-8s [%(filename)s:%(lineno)d] %(message)s'
)

stream_handler = logging.StreamHandler()
stream_handler.setFormatter(formatter)

logger = logging.getLogger()
logger.addHandler(stream_handler)
logger.setLevel(logging.INFO)

logger.info("info logging")

This piece of code produces the following output:

2019-08-21 15:04:55,118,118 INFO     [testHandler.py:11] info logging

Note, I also removed the double brackets on the logger.info call as these are not necessary.

Answer 2

使用 logging.basicConfig() 来初始化日志系统。

Answer 3

You need to set the level of your logger,

logger.setLevel(logging.INFO)

Below statement can be removed from your code,

stream_handler.setLevel(logging.INFO)

Answer 4

A logger and a handler can have different levels. You have only set the level for the handler, not the logger itself.

import logging

formatter = logging.Formatter('%(asctime)s,%(msecs)d %(levelname)-8s [%(filename)s:%(lineno)d] %(message)s')

stream_handler = logging.StreamHandler()
stream_handler.setLevel(logging.INFO)
stream_handler.setFormatter(formatter)

logger = logging.getLogger()
logger.setLevel(logging.INFO)  # Required
logger.addHandler(stream_handler)
logger.info(("info logging"))