Flask logging - Cannot get it to write to a file

Question

Ok, here's the code where I setup everything:

if __name__ == '__main__':     app.debug = False      applogger = app.logger      file_handler = FileHandler("error.log")     file_handler.setLevel(logging.DEBUG)      applogger.setLevel(logging.DEBUG)     applogger.addHandler(file_handler)      app.run(host='0.0.0.0') 

What happens is

1. error.log gets created
2. Nothing is ever written to it
3. Despite not adding a StreamHandler and setting debug to false I still get everything to STDOUT (this might be correct, but still seems weird)

Am I totally off here somewhere or what is happening?

Answer 1

Why not do it like this:

if __name__ == '__main__':     init_db()  # or whatever you need to do      import logging     logging.basicConfig(filename='error.log',level=logging.DEBUG)      app.run(host="0.0.0.0") 

If you now start you application, you'll see that error.log contains:

INFO:werkzeug: * Running on http://0.0.0.0:5000/ 

For more info, visit http://docs.python.org/2/howto/logging.html

Okay, as you insist that you cannot have two handler with the method I showed you, I'll add an example that makes this quite clear. First, add this logging code to your main:

import logging, logging.config, yaml logging.config.dictConfig(yaml.load(open('logging.conf'))) 

Now also add some debug code, so that we see that our setup works:

logfile    = logging.getLogger('file') logconsole = logging.getLogger('console') logfile.debug("Debug FILE") logconsole.debug("Debug CONSOLE") 

All what is left is the "logging.conf" program. Let's use that:

version: 1 formatters:   hiformat:     format: 'HI %(asctime)s - %(name)s - %(levelname)s - %(message)s'   simple:     format: '%(asctime)s - %(name)s - %(levelname)s - %(message)s' handlers:   console:     class: logging.StreamHandler     level: DEBUG     formatter: hiformat     stream: ext://sys.stdout   file:     class: logging.FileHandler     level: DEBUG     formatter: simple     filename: errors.log loggers:   console:     level: DEBUG     handlers: [console]     propagate: no   file:     level: DEBUG     handlers: [file]     propagate: no root:   level: DEBUG   handlers: [console,file] 

This config is more complicated than needed, but it also shows some features of the logging module.

Now, when we run our application, we see this output (werkzeug- and console-logger):

HI 2013-07-22 16:36:13,475 - console - DEBUG - Debug CONSOLE HI 2013-07-22 16:36:13,477 - werkzeug - INFO -  * Running on http://0.0.0.0:5000/ 

Also note that the custom formatter with the "HI" was used.

Now look at the "errors.log" file. It contains:

2013-07-22 16:36:13,475 - file - DEBUG - Debug FILE 2013-07-22 16:36:13,477 - werkzeug - INFO -  * Running on http://0.0.0.0:5000/ 

Answer 2

Ok, my failure stemmed from two misconceptions:

1) Flask will apparently ignore all your custom logging unless it is running in production mode

2) debug=False is not enough to let it run in production mode. You have to wrap the app in any sort of WSGI server to do so

After i started the app from gevent's WSGI server (and moving logging initialization to a more appropriate place) everything seems to work fine