How to redirect logging to files in a CherryPy app

[Wissperwind]

Hi,

I use cherrypy in a windows service.
I have redirected stdout and stderr to files:

    sys.stdout = open(os.path.join(pathOfThisScript, "stdOut.txt"), "w")
    sys.stderr = open(os.path.join(pathOfThisScript, "stdErr.txt"), "w")

I think cherrpy doesn't care about that and is still writing to stdout.
I noticed this by running my service in debug mode where I can see stdout and error.
All other prints go to my files, except the cherrypy starting prints were still displayed on the screen:

[29/Mar/2021:15:12:27] ENGINE Bus STARTING
[29/Mar/2021:15:12:27] ENGINE Started monitor thread 'Autoreloader'.
[29/Mar/2021:15:12:28] ENGINE Serving on http://127.0.0.1:8000
[29/Mar/2021:15:12:28] ENGINE Bus STARTED

This becomes worse if I run the service as a real service. In that case there is no stdout and error. But cherrypy still tries to write to them and produces exceptions that were written to my stderr file. They are repeated many times:

--- Logging error ---
Traceback (most recent call last):
  File "C:\Python39\lib\logging\__init__.py", line 1082, in emit
    stream.write(msg + self.terminator)
AttributeError: 'NoneType' object has no attribute 'write'
Call stack:
  File "C:\Python39\lib\site-packages\win32\lib\win32serviceutil.py", line 839, in SvcRun
    self.SvcDoRun()
  File "C:\GlobalX_Installation\globalx\psbp\psProofDjango\bpservice3.py", line 97, in SvcDoRun
    cherrypy.engine.start()
  File "C:\Python39\lib\site-packages\cherrypy\process\wspbus.py", line 266, in start
    self.log('Bus STARTING')
  File "C:\Python39\lib\site-packages\cherrypy\process\wspbus.py", line 584, in log
    self.publish('log', msg, level)
  File "C:\Python39\lib\site-packages\cherrypy\process\wspbus.py", line 230, in publish
    output.append(listener(*args, **kwargs))
  File "C:\Python39\lib\site-packages\cherrypy\__init__.py", line 352, in _buslog
    log.error(msg, 'ENGINE', severity=level)
  File "C:\Python39\lib\site-packages\cherrypy\_cplogging.py", line 213, in error
    self.error_log.log(
Message: '[29/Mar/2021:17:25:06] ENGINE Bus STARTING'
Arguments: ()

Can you please make cherrypy notice that I have redirected stdout and err?
I also have set the log.error_file config parameter to a file. But to be precise, the error above is printed to my stderror file.

[webknjaz]

Sounds like you patched stderr/out after CherryPy got the pointers to the old objects. Also, I think patching global objects like that is rather bad.

FWIW it sounds like you forgot to configure or disable logging per https://docs.cherrypy.org/en/latest/basics.html#logging:

from pathlib import Path

THIS_SCRIPT_DIR = Path(__file__).parent.resolve()

cherrypy.config.update({
    'log.screen': False,
    'log.access_file': str(THIS_SCRIPT_DIR / 'stdOut.txt'),
    'log.error_file': str(THIS_SCRIPT_DIR / 'stdErr.txt'),
})

Also, note that you could set the environment to production per https://docs.cherrypy.org/en/latest/config.html#environments and that sets 'log.screen': False by default:

cherrypy.config.update({'environment': 'production'})