Python logger with custom handler emits to std

Question

I've created a logger with the custom handler which emits message to telegram via bot. It works, but for some reason the message is also emitted to stderr (or stdout).

My code:

class TelegramHandler(logging.Handler):
    def emit(self, record):
        log_entry = self.format(record)
        payload = {
            'chat_id': TELEGRAM_CHAT_ID,
            'text': log_entry,
            'parse_mode': 'HTML'
        }
        return requests.post("https://api.telegram.org/bot{token}/sendMessage".format(token=TELEGRAM_TOKEN),
                             data=payload).content

# setting up root logger
logging.basicConfig(format='%(asctime)s - %(name)s - %(levelname)s - %(message)s', level=logging.WARNING)

# setting up my logger
logger_bot = logging.getLogger('bot')
handler = TelegramHandler()
logger_bot.addHandler(handler)
logger_bot.setLevel(logging.DEBUG)

And the following code:

logger_bot.info('bot test')
logging.warning('root test')

results in

2019-12-06 22:24:14,401 - bot - INFO - bot test # *(plus message in telegram)*
2019-12-06 22:24:14,740 - root - WARNING - root test

I've checked handlers

for h in logger_bot.handlers:
    print(h)

and only one is present

<TelegramHandler (NOTSET)>

Also noticed when I don't set up root logger, bot logger doesn't emit to std. So those are somehow connected, but I can't figure out what is going on exactly.

Thank you.

Answer 1

You need to set the propagate attribute on the bot logger to False .

So add logger_bot.propagate = False somewhere in the setup for it, and that should cause each log to only be handled by its own handlers.