[FIXED] Exception in coroutine not shown if enable file logging

Issue

I minimal my problem as next:

logger.conf:

###################################
[loggers]
keys=root
[logger_root]
level=DEBUG
handlers=handlerScreen,handlerFile

###################################
[handlers]
keys=handlerScreen,handlerFile
[handler_handlerScreen]
class=StreamHandler
level=DEBUG
formatter=formScreen
args=(sys.stderr,)
[handler_handlerFile]
class=FileHandler
level=INFO
formatter=formFile
args=('%(log_file)s', 'a')

###################################
[formatters]
keys=formScreen,formFile
[formatter_formScreen]
format=%(asctime)s %(message)s
datefmt=%Y-%m-%d %H:%M:%S
[formatter_formFile]
format=%(asctime)s %(filename)-21s[line:%(lineno)-3d] %(levelname)s %(message)s
datefmt=%Y-%m-%d %H:%M:%S

fc.py:

import asyncio
import logging.config

logging.config.fileConfig("logger.conf", defaults=dict(log_file="run.log"))

async def fun():
    print("1")
    1/0
    print("2")

async def action():
    asyncio.create_task(fun())
    print("do other tasks at once")
    await asyncio.sleep(5)

asyncio.run(action())

Execution:

$ python3 fc.py
do other tasks at once
1

Question:

You could see 1/0 didn't print any error in screen, but as 2 not be print, so I guess the exception already happen, just I can't see anything in screen, why could that happen?

What I have tried?

1. Disable file logging:

   import asyncio
   import logging.config
   
   # Disable file logging
   # logging.config.fileConfig("logger.conf", defaults=dict(log_file="run.log"))
   
   async def fun():
       print("1")
       1/0
       print("2")
   
   async def action():
       asyncio.create_task(fun())
       print("do other tasks at once")
       await asyncio.sleep(5)
   
   asyncio.run(action())
   

   Then it run as next:

   $ python3 fc.py
   do other tasks at once
   1
   Task exception was never retrieved
   future: <Task finished name='Task-2' coro=<fun() done, defined at fc.py:6> 
   exception=ZeroDivisionError('division by zero')>
   Traceback (most recent call last):
     File "fc.py", line 9, in fun
       1/0
   ZeroDivisionError: division by zero
   

2. Add try...except:

   import asyncio
   import logging.config
   
   logging.config.fileConfig("logger.conf", defaults=dict(log_file="run.log"))
   
   async def fun():
       print("1")
       try:
           1/0
       except Exception as e:
           print(e)
       print("2")
   
   async def action():
       asyncio.create_task(fun())
       print("do other tasks at once")
       await asyncio.sleep(5)
   
   asyncio.run(action())
   

   Then, it run as next:

   $ python3 fc.py
   do other tasks at once
   1
   division by zero
   2
   

So, how can I make the error be shown without disable file logging, meanwhile without using explicit try...catch? If I could know why my situation happen, that will be better.

NOTE: await asyncio.create_task(fun()) is not what I need. In my scenario, I can't wait fun be finished then do next actions. I use Python 3.8.10 if that mattered.

Solution

After check the source of asyncio, I got the reason: asyncio also use logging to print the exception:

asyncio/log.py:

import logging
logger = logging.getLogger(__package__)

asyncio/base_events.py:

def default_exception_handler(self, context):
    """Default exception handler.

    This is called when an exception occurs and no exception
    handler is set, and can be called by a custom exception
    handler that wants to defer to the default behavior.

    ......
    """
    ......
    logger.error('\n'.join(log_lines), exc_info=exc_info)

So, asyncio define a logger with name "asyncio" (__package__). However, in my logger.conf, I just define a logger with keys=root, this is the reason the error not be shown to screen.

So, change logger.conf to next could work, although I didn't know how to let logger.conf default handle all logger without explictly specify them:

##################################
[loggers]
keys=root,asyncio
[logger_root]
level=DEBUG
handlers=handlerScreen,handlerFile
[logger_asyncio]
level=DEBUG
qualname=asyncio
handlers=handlerScreen,handlerFile

Answered By - atline